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 $66.78   9.809%   $73.3305   $73.33   $73.35   $73.30  
  Purchase #2 $48.80   6.746%   $52.092   $52.09   $52.10   $52.10  
  Purchase #3 $235.43   4.648%   $246.3728   $246.37   $246.35   $246.40  
  Purchase #4 $119.30   5.274%   $125.5919   $125.59   $125.60   $125.60  
  Purchase #5 $68.52   8.676%   $74.4648   $74.46   $74.45   $74.50  
  Purchase #6 $161.56   9.209%   $176.4381   $176.44   $176.45   $176.40  
  Purchase #7 $8.47   9.541%   $9.2781   $9.28   $9.30   $9.30  
  7 purchase totals = $708.86       $757.5682   $757.56   $757.60   $757.60