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 $61.51   11.682%   $68.6956   $68.70   $68.70   $68.70  
  Purchase #2 $86.82   8.220%   $93.9566   $93.96   $93.95   $94.00  
  Purchase #3 $207.86   7.446%   $223.3373   $223.34   $223.35   $223.30  
  Purchase #4 $122.72   13.443%   $139.2172   $139.22   $139.20   $139.20  
  Purchase #5 $92.87   11.287%   $103.3522   $103.35   $103.35   $103.40  
  Purchase #6 $154.56   6.230%   $164.1891   $164.19   $164.20   $164.20  
  Purchase #7 $130.69   8.148%   $141.3386   $141.34   $141.35   $141.30  
  7 purchase totals = $857.03       $934.0866   $934.10   $934.10   $934.10