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 $83.30   12.475%   $93.6917   $93.69   $93.70   $93.70  
  Purchase #2 $164.94   11.435%   $183.8009   $183.80   $183.80   $183.80  
  Purchase #3 $244.47   5.246%   $257.2949   $257.29   $257.30   $257.30  
  Purchase #4 $230.38   6.611%   $245.6104   $245.61   $245.60   $245.60  
  Purchase #5 $156.40   3.396%   $161.7113   $161.71   $161.70   $161.70  
  Purchase #6 $31.67   7.220%   $33.9566   $33.96   $33.95   $34.00  
  Purchase #7 $55.29   12.636%   $62.2764   $62.28   $62.30   $62.30  
  7 purchase totals = $966.45       $1,038.3422   $1,038.34   $1,038.35   $1,038.40