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 $195.51   3.491%   $202.3353   $202.34   $202.35   $202.30  
  Purchase #2 $72.98   3.738%   $75.708   $75.71   $75.70   $75.70  
  Purchase #3 $233.65   8.727%   $254.0406   $254.04   $254.05   $254.00  
  Purchase #4 $210.96   10.307%   $232.7036   $232.70   $232.70   $232.70  
  Purchase #5 $89.41   7.377%   $96.0058   $96.01   $96.00   $96.00  
  Purchase #6 $151.66   9.297%   $165.7598   $165.76   $165.75   $165.80  
  Purchase #7 $211.45   3.454%   $218.7535   $218.75   $218.75   $218.80  
  7 purchase totals = $1,165.62       $1,245.3066   $1,245.31   $1,245.30   $1,245.30