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 $127.25   6.719%   $135.7999   $135.80   $135.80   $135.80  
  Purchase #2 $87.92   13.564%   $99.8455   $99.85   $99.85   $99.80  
  Purchase #3 $150.80   8.788%   $164.0523   $164.05   $164.05   $164.10  
  Purchase #4 $225.76   7.781%   $243.3264   $243.33   $243.35   $243.30  
  Purchase #5 $156.37   12.544%   $175.9851   $175.99   $176.00   $176.00  
  Purchase #6 $25.60   6.468%   $27.2558   $27.26   $27.25   $27.30  
  Purchase #7 $152.28   8.261%   $164.8599   $164.86   $164.85   $164.90  
  7 purchase totals = $925.98       $1,011.1249   $1,011.14   $1,011.15   $1,011.20