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 $250.46   10.107%   $275.774   $275.77   $275.75   $275.80  
  Purchase #2 $82.51   13.817%   $93.9104   $93.91   $93.90   $93.90  
  Purchase #3 $212.82   10.230%   $234.5915   $234.59   $234.60   $234.60  
  Purchase #4 $169.48   3.104%   $174.7407   $174.74   $174.75   $174.70  
  Purchase #5 $216.82   13.748%   $246.6284   $246.63   $246.65   $246.60  
  Purchase #6 $44.39   7.151%   $47.5643   $47.56   $47.55   $47.60  
  Purchase #7 $207.54   6.825%   $221.7046   $221.70   $221.70   $221.70  
  7 purchase totals = $1,184.02       $1,294.9139   $1,294.90   $1,294.90   $1,294.90