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 $63.87   4.817%   $66.9466   $66.95   $66.95   $66.90  
  Purchase #2 $236.39   7.683%   $254.5518   $254.55   $254.55   $254.60  
  Purchase #3 $236.35   7.813%   $254.816   $254.82   $254.80   $254.80  
  Purchase #4 $237.59   11.276%   $264.3806   $264.38   $264.40   $264.40  
  Purchase #5 $80.50   12.573%   $90.6213   $90.62   $90.60   $90.60  
  Purchase #6 $136.80   10.278%   $150.8603   $150.86   $150.85   $150.90  
  Purchase #7 $113.75   10.278%   $125.4412   $125.44   $125.45   $125.40  
  7 purchase totals = $1,105.25       $1,207.6178   $1,207.62   $1,207.60   $1,207.60