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 $24.38   5.790%   $25.7916   $25.79   $25.80   $25.80  
  Purchase #2 $205.46   11.729%   $229.5584   $229.56   $229.55   $229.60  
  Purchase #3 $44.28   11.252%   $49.2624   $49.26   $49.25   $49.30  
  Purchase #4 $245.35   6.463%   $261.207   $261.21   $261.20   $261.20  
  Purchase #5 $202.67   13.318%   $229.6616   $229.66   $229.65   $229.70  
  Purchase #6 $42.68   3.719%   $44.2673   $44.27   $44.25   $44.30  
  Purchase #7 $44.38   3.283%   $45.837   $45.84   $45.85   $45.80  
  7 purchase totals = $809.20       $885.5853   $885.59   $885.55   $885.70