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 $141.51   11.188%   $157.3421   $157.34   $157.35   $157.30  
  Purchase #2 $183.51   6.170%   $194.8326   $194.83   $194.85   $194.80  
  Purchase #3 $204.29   5.674%   $215.8814   $215.88   $215.90   $215.90  
  Purchase #4 $24.50   3.630%   $25.3894   $25.39   $25.40   $25.40  
  Purchase #5 $114.62   10.499%   $126.654   $126.65   $126.65   $126.70  
  Purchase #6 $207.30   4.716%   $217.0763   $217.08   $217.10   $217.10  
  Purchase #7 $112.50   5.148%   $118.2915   $118.29   $118.30   $118.30  
  7 purchase totals = $988.23       $1,055.4673   $1,055.46   $1,055.55   $1,055.50