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 $244.95   7.254%   $262.7187   $262.72   $262.70   $262.70  
  Purchase #2 $150.62   4.646%   $157.6178   $157.62   $157.60   $157.60  
  Purchase #3 $57.53   8.141%   $62.2135   $62.21   $62.20   $62.20  
  Purchase #4 $13.82   10.219%   $15.2323   $15.23   $15.25   $15.20  
  Purchase #5 $171.29   12.287%   $192.3364   $192.34   $192.35   $192.30  
  Purchase #6 $206.98   13.427%   $234.7712   $234.77   $234.75   $234.80  
  Purchase #7 $146.29   4.217%   $152.459   $152.46   $152.45   $152.50  
  7 purchase totals = $991.48       $1,077.3489   $1,077.35   $1,077.30   $1,077.30