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 $154.99   7.266%   $166.2516   $166.25   $166.25   $166.30  
  Purchase #2 $141.39   7.396%   $151.8472   $151.85   $151.85   $151.80  
  Purchase #3 $41.77   7.577%   $44.9349   $44.93   $44.95   $44.90  
  Purchase #4 $231.26   5.711%   $244.4673   $244.47   $244.45   $244.50  
  Purchase #5 $173.88   4.653%   $181.9706   $181.97   $181.95   $182.00  
  Purchase #6 $80.51   3.439%   $83.2787   $83.28   $83.30   $83.30  
  Purchase #7 $71.95   12.206%   $80.7322   $80.73   $80.75   $80.70  
  7 purchase totals = $895.75       $953.4825   $953.48   $953.50   $953.50