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 $111.61   6.257%   $118.5934   $118.59   $118.60   $118.60  
  Purchase #2 $20.35   6.763%   $21.7263   $21.73   $21.75   $21.70  
  Purchase #3 $160.55   5.750%   $169.7816   $169.78   $169.80   $169.80  
  Purchase #4 $29.39   6.731%   $31.3682   $31.37   $31.35   $31.40  
  Purchase #5 $197.84   5.751%   $209.2178   $209.22   $209.20   $209.20  
  Purchase #6 $116.77   6.301%   $124.1277   $124.13   $124.15   $124.10  
  Purchase #7 $64.69   3.450%   $66.9218   $66.92   $66.90   $66.90  
  7 purchase totals = $701.20       $741.7368   $741.74   $741.75   $741.70