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 $113.28   11.191%   $125.9572   $125.96   $125.95   $126.00  
  Purchase #2 $61.28   10.702%   $67.8382   $67.84   $67.85   $67.80  
  Purchase #3 $39.45   4.400%   $41.1858   $41.19   $41.20   $41.20  
  Purchase #4 $170.31   8.130%   $184.1562   $184.16   $184.15   $184.20  
  Purchase #5 $240.69   13.498%   $273.1783   $273.18   $273.20   $273.20  
  Purchase #6 $101.70   11.555%   $113.4514   $113.45   $113.45   $113.50  
  Purchase #7 $131.88   6.240%   $140.1093   $140.11   $140.10   $140.10  
  7 purchase totals = $858.59       $945.8764   $945.89   $945.90   $946.00