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 $81.74   7.713%   $88.0446   $88.04   $88.05   $88.00  
  Purchase #2 $216.96   13.135%   $245.4577   $245.46   $245.45   $245.50  
  Purchase #3 $196.38   5.220%   $206.631   $206.63   $206.65   $206.60  
  Purchase #4 $79.77   6.500%   $84.9551   $84.96   $84.95   $85.00  
  Purchase #5 $230.37   13.587%   $261.6704   $261.67   $261.65   $261.70  
  Purchase #6 $218.50   9.627%   $239.535   $239.54   $239.55   $239.50  
  Purchase #7 $151.76   5.212%   $159.6697   $159.67   $159.65   $159.70  
  7 purchase totals = $1,175.48       $1,285.9635   $1,285.97   $1,285.95   $1,286.00