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 $148.36   7.319%   $159.2185   $159.22   $159.20   $159.20  
  Purchase #2 $183.51   12.244%   $205.979   $205.98   $206.00   $206.00  
  Purchase #3 $118.97   10.549%   $131.5201   $131.52   $131.50   $131.50  
  Purchase #4 $118.70   6.144%   $125.9929   $125.99   $126.00   $126.00  
  Purchase #5 $16.50   7.176%   $17.684   $17.68   $17.70   $17.70  
  Purchase #6 $126.32   6.817%   $134.9312   $134.93   $134.95   $134.90  
  Purchase #7 $123.98   9.683%   $135.985   $135.99   $136.00   $136.00  
  7 purchase totals = $836.34       $911.3107   $911.31   $911.35   $911.30