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 $88.59   10.143%   $97.5757   $97.58   $97.60   $97.60  
  Purchase #2 $135.91   9.132%   $148.3213   $148.32   $148.30   $148.30  
  Purchase #3 $97.25   7.797%   $104.8326   $104.83   $104.85   $104.80  
  Purchase #4 $147.69   5.417%   $155.6904   $155.69   $155.70   $155.70  
  Purchase #5 $241.69   10.180%   $266.294   $266.29   $266.30   $266.30  
  Purchase #6 $87.37   13.110%   $98.8242   $98.82   $98.80   $98.80  
  Purchase #7 $137.69   9.811%   $151.1988   $151.20   $151.20   $151.20  
  7 purchase totals = $936.19       $1,022.7370   $1,022.73   $1,022.75   $1,022.70