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 $111.68   13.326%   $126.5625   $126.56   $126.55   $126.60  
  Purchase #2 $203.35   11.698%   $227.1379   $227.14   $227.15   $227.10  
  Purchase #3 $159.78   9.170%   $174.4318   $174.43   $174.45   $174.40  
  Purchase #4 $47.41   9.233%   $51.7874   $51.79   $51.80   $51.80  
  Purchase #5 $201.25   4.569%   $210.4451   $210.45   $210.45   $210.40  
  Purchase #6 $202.92   11.191%   $225.6288   $225.63   $225.65   $225.60  
  Purchase #7 $234.49   5.368%   $247.0774   $247.08   $247.10   $247.10  
  7 purchase totals = $1,160.88       $1,263.0709   $1,263.08   $1,263.15   $1,263.00