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 $87.25   13.170%   $98.7408   $98.74   $98.75   $98.70  
  Purchase #2 $232.89   10.632%   $257.6509   $257.65   $257.65   $257.70  
  Purchase #3 $34.37   8.254%   $37.2069   $37.21   $37.20   $37.20  
  Purchase #4 $237.40   3.191%   $244.9754   $244.98   $245.00   $245.00  
  Purchase #5 $168.38   9.832%   $184.9351   $184.94   $184.95   $184.90  
  Purchase #6 $58.93   13.638%   $66.9669   $66.97   $66.95   $67.00  
  Purchase #7 $100.33   7.523%   $107.8778   $107.88   $107.90   $107.90  
  7 purchase totals = $919.55       $998.3538   $998.37   $998.40   $998.40