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 $59.87   6.753%   $63.913   $63.91   $63.90   $63.90  
  Purchase #2 $16.29   6.473%   $17.3445   $17.34   $17.35   $17.30  
  Purchase #3 $196.75   10.496%   $217.4009   $217.40   $217.40   $217.40  
  Purchase #4 $138.42   7.826%   $149.2527   $149.25   $149.25   $149.30  
  Purchase #5 $181.80   12.662%   $204.8195   $204.82   $204.80   $204.80  
  Purchase #6 $36.97   10.452%   $40.8341   $40.83   $40.85   $40.80  
  Purchase #7 $83.39   11.310%   $92.8214   $92.82   $92.80   $92.80  
  7 purchase totals = $713.49       $786.3861   $786.37   $786.35   $786.30