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 $147.66   13.478%   $167.5616   $167.56   $167.55   $167.60  
  Purchase #2 $216.75   10.245%   $238.956   $238.96   $238.95   $239.00  
  Purchase #3 $140.42   6.545%   $149.6105   $149.61   $149.60   $149.60  
  Purchase #4 $163.85   8.352%   $177.5348   $177.53   $177.55   $177.50  
  Purchase #5 $97.80   8.685%   $106.2939   $106.29   $106.30   $106.30  
  Purchase #6 $110.68   12.458%   $124.4685   $124.47   $124.45   $124.50  
  Purchase #7 $46.96   8.689%   $51.0404   $51.04   $51.05   $51.00  
  7 purchase totals = $924.12       $1,015.4657   $1,015.46   $1,015.45   $1,015.50