Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $110.62   11.848%   $123.7263   $123.73   $123.75   $123.70  
  Purchase #2 $147.28   10.675%   $163.0021   $163.00   $163.00   $163.00  
  Purchase #3 $191.30   11.332%   $212.9781   $212.98   $213.00   $213.00  
  Purchase #4 $131.31   8.240%   $142.1299   $142.13   $142.15   $142.10  
  Purchase #5 $111.53   11.856%   $124.753   $124.75   $124.75   $124.80  
  Purchase #6 $199.31   12.211%   $223.6477   $223.65   $223.65   $223.60  
  Purchase #7 $231.80   11.767%   $259.0759   $259.08   $259.10   $259.10  
  7 purchase totals = $1,123.15       $1,249.3130   $1,249.32   $1,249.40   $1,249.30