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 $213.49   11.588%   $238.2292   $238.23   $238.25   $238.20  
  Purchase #2 $174.67   13.315%   $197.9273   $197.93   $197.95   $197.90  
  Purchase #3 $151.78   7.123%   $162.5913   $162.59   $162.60   $162.60  
  Purchase #4 $160.28   3.222%   $165.4442   $165.44   $165.45   $165.40  
  Purchase #5 $54.72   13.829%   $62.2872   $62.29   $62.30   $62.30  
  Purchase #6 $97.56   9.771%   $107.0926   $107.09   $107.10   $107.10  
  Purchase #7 $214.87   10.424%   $237.268   $237.27   $237.25   $237.30  
  7 purchase totals = $1,067.37       $1,170.8398   $1,170.84   $1,170.90   $1,170.80