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 $112.39   4.840%   $117.8297   $117.83   $117.85   $117.80  
  Purchase #2 $247.81   4.856%   $259.8437   $259.84   $259.85   $259.80  
  Purchase #3 $151.36   5.508%   $159.6969   $159.70   $159.70   $159.70  
  Purchase #4 $139.33   4.267%   $145.2752   $145.28   $145.30   $145.30  
  Purchase #5 $246.79   5.326%   $259.934   $259.93   $259.95   $259.90  
  Purchase #6 $72.32   3.623%   $74.9402   $74.94   $74.95   $74.90  
  Purchase #7 $27.64   3.851%   $28.7044   $28.70   $28.70   $28.70  
  7 purchase totals = $997.64       $1,046.2241   $1,046.22   $1,046.30   $1,046.10