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 $63.79   6.823%   $68.1424   $68.14   $68.15   $68.10  
  Purchase #2 $242.74   7.381%   $260.6566   $260.66   $260.65   $260.70  
  Purchase #3 $201.57   8.542%   $218.7881   $218.79   $218.80   $218.80  
  Purchase #4 $146.72   7.265%   $157.3792   $157.38   $157.40   $157.40  
  Purchase #5 $29.29   11.577%   $32.6809   $32.68   $32.70   $32.70  
  Purchase #6 $156.51   9.605%   $171.5428   $171.54   $171.55   $171.50  
  Purchase #7 $144.92   4.828%   $151.9167   $151.92   $151.90   $151.90  
  7 purchase totals = $985.54       $1,061.1067   $1,061.11   $1,061.15   $1,061.10