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 $112.37   11.866%   $125.7038   $125.70   $125.70   $125.70  
  Purchase #2 $87.56   4.711%   $91.685   $91.69   $91.70   $91.70  
  Purchase #3 $69.51   9.415%   $76.0544   $76.05   $76.05   $76.10  
  Purchase #4 $34.43   9.155%   $37.5821   $37.58   $37.60   $37.60  
  Purchase #5 $135.58   6.871%   $144.8957   $144.90   $144.90   $144.90  
  Purchase #6 $111.91   8.517%   $121.4414   $121.44   $121.45   $121.40  
  Purchase #7 $11.34   5.693%   $11.9856   $11.99   $12.00   $12.00  
  7 purchase totals = $562.70       $609.3480   $609.35   $609.40   $609.40