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 $46.63   7.356%   $50.0601   $50.06   $50.05   $50.10  
  Purchase #2 $241.85   6.284%   $257.0479   $257.05   $257.05   $257.00  
  Purchase #3 $37.29   7.699%   $40.161   $40.16   $40.15   $40.20  
  Purchase #4 $59.53   8.387%   $64.5228   $64.52   $64.50   $64.50  
  Purchase #5 $207.96   7.247%   $223.0309   $223.03   $223.05   $223.00  
  Purchase #6 $194.84   12.865%   $219.9062   $219.91   $219.90   $219.90  
  Purchase #7 $234.32   11.483%   $261.227   $261.23   $261.25   $261.20  
  7 purchase totals = $1,022.42       $1,115.9559   $1,115.96   $1,115.95   $1,115.90