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 $178.29   12.738%   $201.0006   $201.00   $201.00   $201.00  
  Purchase #2 $245.58   9.283%   $268.3772   $268.38   $268.40   $268.40  
  Purchase #3 $113.34   10.727%   $125.498   $125.50   $125.50   $125.50  
  Purchase #4 $94.83   8.295%   $102.6961   $102.70   $102.70   $102.70  
  Purchase #5 $48.73   12.587%   $54.8636   $54.86   $54.85   $54.90  
  Purchase #6 $205.43   10.574%   $227.1522   $227.15   $227.15   $227.20  
  Purchase #7 $65.35   12.395%   $73.4501   $73.45   $73.45   $73.50  
  7 purchase totals = $951.55       $1,053.0378   $1,053.04   $1,053.05   $1,053.20