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 $40.61   7.524%   $43.6655   $43.67   $43.65   $43.70  
  Purchase #2 $230.84   12.820%   $260.4337   $260.43   $260.45   $260.40  
  Purchase #3 $50.53   7.580%   $54.3602   $54.36   $54.35   $54.40  
  Purchase #4 $130.69   4.563%   $136.6534   $136.65   $136.65   $136.70  
  Purchase #5 $120.67   10.801%   $133.7036   $133.70   $133.70   $133.70  
  Purchase #6 $250.46   12.392%   $281.497   $281.50   $281.50   $281.50  
  Purchase #7 $43.34   11.814%   $48.4602   $48.46   $48.45   $48.50  
  7 purchase totals = $867.14       $958.7736   $958.77   $958.75   $958.90