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 $152.46   11.647%   $170.217   $170.22   $170.20   $170.20  
  Purchase #2 $94.44   13.774%   $107.4482   $107.45   $107.45   $107.40  
  Purchase #3 $126.47   9.672%   $138.7022   $138.70   $138.70   $138.70  
  Purchase #4 $233.74   10.166%   $257.502   $257.50   $257.50   $257.50  
  Purchase #5 $88.38   11.283%   $98.3519   $98.35   $98.35   $98.40  
  Purchase #6 $203.94   10.177%   $224.695   $224.70   $224.70   $224.70  
  Purchase #7 $156.31   11.513%   $174.306   $174.31   $174.30   $174.30  
  7 purchase totals = $1,055.74       $1,171.2223   $1,171.23   $1,171.20   $1,171.20