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 $45.27   6.474%   $48.2008   $48.20   $48.20   $48.20  
  Purchase #2 $211.77   13.286%   $239.9058   $239.91   $239.90   $239.90  
  Purchase #3 $182.94   12.373%   $205.5752   $205.58   $205.60   $205.60  
  Purchase #4 $135.84   7.861%   $146.5184   $146.52   $146.50   $146.50  
  Purchase #5 $94.69   11.204%   $105.2991   $105.30   $105.30   $105.30  
  Purchase #6 $195.50   6.343%   $207.9006   $207.90   $207.90   $207.90  
  Purchase #7 $169.28   13.290%   $191.7773   $191.78   $191.80   $191.80  
  7 purchase totals = $1,035.29       $1,145.1772   $1,145.19   $1,145.20   $1,145.20