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 $241.95   12.596%   $272.426   $272.43   $272.45   $272.40  
  Purchase #2 $20.41   13.284%   $23.1213   $23.12   $23.10   $23.10  
  Purchase #3 $33.88   7.533%   $36.4322   $36.43   $36.45   $36.40  
  Purchase #4 $145.95   3.683%   $151.3253   $151.33   $151.35   $151.30  
  Purchase #5 $219.28   6.643%   $233.8468   $233.85   $233.85   $233.80  
  Purchase #6 $101.54   6.736%   $108.3797   $108.38   $108.40   $108.40  
  Purchase #7 $211.57   11.706%   $236.3364   $236.34   $236.35   $236.30  
  7 purchase totals = $974.58       $1,061.8677   $1,061.88   $1,061.95   $1,061.70