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 $118.95   10.144%   $131.0163   $131.02   $131.00   $131.00  
  Purchase #2 $176.72   12.730%   $199.2165   $199.22   $199.20   $199.20  
  Purchase #3 $150.95   11.245%   $167.9243   $167.92   $167.90   $167.90  
  Purchase #4 $101.40   8.773%   $110.2958   $110.30   $110.30   $110.30  
  Purchase #5 $27.51   10.411%   $30.3741   $30.37   $30.35   $30.40  
  Purchase #6 $51.65   8.376%   $55.9762   $55.98   $56.00   $56.00  
  Purchase #7 $240.77   9.215%   $262.957   $262.96   $262.95   $263.00  
  7 purchase totals = $867.95       $957.7602   $957.77   $957.70   $957.80