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 $63.61   7.317%   $68.2643   $68.26   $68.25   $68.30  
  Purchase #2 $189.32   4.173%   $197.2203   $197.22   $197.20   $197.20  
  Purchase #3 $176.65   10.754%   $195.6469   $195.65   $195.65   $195.60  
  Purchase #4 $14.99   7.301%   $16.0844   $16.08   $16.10   $16.10  
  Purchase #5 $84.43   10.601%   $93.3804   $93.38   $93.40   $93.40  
  Purchase #6 $112.85   12.337%   $126.7723   $126.77   $126.75   $126.80  
  Purchase #7 $65.96   4.379%   $68.8484   $68.85   $68.85   $68.80  
  7 purchase totals = $707.81       $766.2170   $766.21   $766.20   $766.20