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 $205.42   8.417%   $222.7102   $222.71   $222.70   $222.70  
  Purchase #2 $49.75   4.461%   $51.9693   $51.97   $51.95   $52.00  
  Purchase #3 $19.66   4.115%   $20.469   $20.47   $20.45   $20.50  
  Purchase #4 $60.35   6.858%   $64.4888   $64.49   $64.50   $64.50  
  Purchase #5 $206.30   6.869%   $220.4707   $220.47   $220.45   $220.50  
  Purchase #6 $154.75   7.557%   $166.4445   $166.44   $166.45   $166.40  
  Purchase #7 $12.63   13.316%   $14.3118   $14.31   $14.30   $14.30  
  7 purchase totals = $708.86       $760.8643   $760.86   $760.80   $760.90