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 $246.56   5.835%   $260.9468   $260.95   $260.95   $260.90  
  Purchase #2 $29.70   13.136%   $33.6014   $33.60   $33.60   $33.60  
  Purchase #3 $199.76   4.700%   $209.1487   $209.15   $209.15   $209.10  
  Purchase #4 $56.67   10.570%   $62.66   $62.66   $62.65   $62.70  
  Purchase #5 $202.96   3.425%   $209.9114   $209.91   $209.90   $209.90  
  Purchase #6 $188.62   3.807%   $195.8008   $195.80   $195.80   $195.80  
  Purchase #7 $95.55   12.819%   $107.7986   $107.80   $107.80   $107.80  
  7 purchase totals = $1,019.82       $1,079.8677   $1,079.87   $1,079.85   $1,079.80