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 $29.42   10.554%   $32.525   $32.53   $32.55   $32.50  
  Purchase #2 $60.46   10.103%   $66.5683   $66.57   $66.55   $66.60  
  Purchase #3 $178.52   3.444%   $184.6682   $184.67   $184.65   $184.70  
  Purchase #4 $201.47   13.306%   $228.2776   $228.28   $228.30   $228.30  
  Purchase #5 $184.49   12.870%   $208.2339   $208.23   $208.25   $208.20  
  Purchase #6 $13.84   6.679%   $14.7644   $14.76   $14.75   $14.80  
  Purchase #7 $218.77   9.297%   $239.109   $239.11   $239.10   $239.10  
  7 purchase totals = $886.97       $974.1464   $974.15   $974.15   $974.20