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 $63.52   8.375%   $68.8398   $68.84   $68.85   $68.80  
  Purchase #2 $181.73   10.269%   $200.3919   $200.39   $200.40   $200.40  
  Purchase #3 $74.67   12.404%   $83.9321   $83.93   $83.95   $83.90  
  Purchase #4 $149.72   6.517%   $159.4773   $159.48   $159.50   $159.50  
  Purchase #5 $61.34   11.191%   $68.2046   $68.20   $68.20   $68.20  
  Purchase #6 $200.87   5.539%   $211.9962   $212.00   $212.00   $212.00  
  Purchase #7 $195.59   4.336%   $204.0708   $204.07   $204.05   $204.10  
  7 purchase totals = $927.44       $996.9127   $996.91   $996.95   $996.90