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 $125.72   5.744%   $132.9414   $132.94   $132.95   $132.90  
  Purchase #2 $71.98   7.862%   $77.6391   $77.64   $77.65   $77.60  
  Purchase #3 $230.92   6.610%   $246.1838   $246.18   $246.20   $246.20  
  Purchase #4 $219.50   4.466%   $229.3029   $229.30   $229.30   $229.30  
  Purchase #5 $61.25   8.267%   $66.3135   $66.31   $66.30   $66.30  
  Purchase #6 $207.53   12.418%   $233.3011   $233.30   $233.30   $233.30  
  Purchase #7 $38.38   9.834%   $42.1543   $42.15   $42.15   $42.20  
  7 purchase totals = $955.28       $1,027.8361   $1,027.82   $1,027.85   $1,027.80