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 $90.96   8.807%   $98.9708   $98.97   $98.95   $99.00  
  Purchase #2 $141.30   5.194%   $148.6391   $148.64   $148.65   $148.60  
  Purchase #3 $85.50   5.489%   $90.1931   $90.19   $90.20   $90.20  
  Purchase #4 $132.82   8.642%   $144.2983   $144.30   $144.30   $144.30  
  Purchase #5 $111.86   12.127%   $125.4253   $125.43   $125.45   $125.40  
  Purchase #6 $182.84   4.367%   $190.8246   $190.82   $190.80   $190.80  
  Purchase #7 $236.72   10.571%   $261.7437   $261.74   $261.75   $261.70  
  7 purchase totals = $982.00       $1,060.0949   $1,060.09   $1,060.10   $1,060.00