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 $46.53   13.298%   $52.7176   $52.72   $52.70   $52.70  
  Purchase #2 $169.38   12.582%   $190.6914   $190.69   $190.70   $190.70  
  Purchase #3 $189.98   13.333%   $215.31   $215.31   $215.30   $215.30  
  Purchase #4 $102.78   3.754%   $106.6384   $106.64   $106.65   $106.60  
  Purchase #5 $243.74   9.111%   $265.9472   $265.95   $265.95   $265.90  
  Purchase #6 $192.28   8.795%   $209.191   $209.19   $209.20   $209.20  
  Purchase #7 $118.25   5.489%   $124.7407   $124.74   $124.75   $124.70  
  7 purchase totals = $1,062.94       $1,165.2363   $1,165.24   $1,165.25   $1,165.10