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 $240.65   11.184%   $267.5643   $267.56   $267.55   $267.60  
  Purchase #2 $29.60   9.152%   $32.309   $32.31   $32.30   $32.30  
  Purchase #3 $108.56   10.284%   $119.7243   $119.72   $119.70   $119.70  
  Purchase #4 $83.90   9.249%   $91.6599   $91.66   $91.65   $91.70  
  Purchase #5 $51.31   6.729%   $54.7626   $54.76   $54.75   $54.80  
  Purchase #6 $172.52   9.146%   $188.2987   $188.30   $188.30   $188.30  
  Purchase #7 $96.54   7.127%   $103.4204   $103.42   $103.40   $103.40  
  7 purchase totals = $783.08       $857.7392   $857.73   $857.65   $857.80