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 $139.53   9.665%   $153.0156   $153.02   $153.00   $153.00  
  Purchase #2 $119.85   4.869%   $125.6855   $125.69   $125.70   $125.70  
  Purchase #3 $137.75   3.514%   $142.5905   $142.59   $142.60   $142.60  
  Purchase #4 $226.39   3.606%   $234.5536   $234.55   $234.55   $234.60  
  Purchase #5 $201.33   8.606%   $218.6565   $218.66   $218.65   $218.70  
  Purchase #6 $96.40   5.784%   $101.9758   $101.98   $102.00   $102.00  
  Purchase #7 $227.84   8.417%   $247.0173   $247.02   $247.00   $247.00  
  7 purchase totals = $1,149.09       $1,223.4948   $1,223.51   $1,223.50   $1,223.60