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 $85.86   12.599%   $96.6775   $96.68   $96.70   $96.70  
  Purchase #2 $66.70   13.186%   $75.4951   $75.50   $75.50   $75.50  
  Purchase #3 $12.67   12.434%   $14.2454   $14.25   $14.25   $14.20  
  Purchase #4 $103.83   6.217%   $110.2851   $110.29   $110.30   $110.30  
  Purchase #5 $245.71   12.107%   $275.4581   $275.46   $275.45   $275.50  
  Purchase #6 $27.91   12.494%   $31.3971   $31.40   $31.40   $31.40  
  Purchase #7 $133.25   3.555%   $137.987   $137.99   $138.00   $138.00  
  7 purchase totals = $675.93       $741.5453   $741.57   $741.60   $741.60