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 $54.77   7.217%   $58.7228   $58.72   $58.70   $58.70  
  Purchase #2 $245.51   13.543%   $278.7594   $278.76   $278.75   $278.80  
  Purchase #3 $180.70   13.430%   $204.968   $204.97   $204.95   $205.00  
  Purchase #4 $84.47   4.732%   $88.4671   $88.47   $88.45   $88.50  
  Purchase #5 $54.65   6.201%   $58.0388   $58.04   $58.05   $58.00  
  Purchase #6 $210.27   11.275%   $233.9779   $233.98   $234.00   $234.00  
  Purchase #7 $46.82   10.698%   $51.8288   $51.83   $51.85   $51.80  
  7 purchase totals = $877.19       $974.7628   $974.77   $974.75   $974.80