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 $180.88   13.284%   $204.9081   $204.91   $204.90   $204.90  
  Purchase #2 $32.57   10.482%   $35.984   $35.98   $36.00   $36.00  
  Purchase #3 $234.83   4.469%   $245.3246   $245.32   $245.30   $245.30  
  Purchase #4 $10.94   11.177%   $12.1628   $12.16   $12.15   $12.20  
  Purchase #5 $95.47   11.107%   $106.0739   $106.07   $106.05   $106.10  
  Purchase #6 $183.39   5.690%   $193.8249   $193.82   $193.80   $193.80  
  Purchase #7 $191.50   12.736%   $215.8894   $215.89   $215.90   $215.90  
  7 purchase totals = $929.58       $1,014.1677   $1,014.15   $1,014.10   $1,014.20