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 $227.30   8.342%   $246.2614   $246.26   $246.25   $246.30  
  Purchase #2 $64.48   12.570%   $72.5851   $72.59   $72.60   $72.60  
  Purchase #3 $188.85   11.196%   $209.9936   $209.99   $210.00   $210.00  
  Purchase #4 $54.66   7.530%   $58.7759   $58.78   $58.80   $58.80  
  Purchase #5 $22.48   9.547%   $24.6262   $24.63   $24.65   $24.60  
  Purchase #6 $198.69   7.836%   $214.2593   $214.26   $214.25   $214.30  
  Purchase #7 $245.72   8.718%   $267.1419   $267.14   $267.15   $267.10  
  7 purchase totals = $1,002.18       $1,093.6434   $1,093.65   $1,093.70   $1,093.70