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 $246.64   11.376%   $274.6978   $274.70   $274.70   $274.70  
  Purchase #2 $204.59   5.188%   $215.2041   $215.20   $215.20   $215.20  
  Purchase #3 $222.28   7.554%   $239.071   $239.07   $239.05   $239.10  
  Purchase #4 $225.90   5.431%   $238.1686   $238.17   $238.15   $238.20  
  Purchase #5 $155.26   10.143%   $171.008   $171.01   $171.00   $171.00  
  Purchase #6 $122.51   10.606%   $135.5034   $135.50   $135.50   $135.50  
  Purchase #7 $54.95   9.715%   $60.2884   $60.29   $60.30   $60.30  
  7 purchase totals = $1,232.13       $1,333.9413   $1,333.94   $1,333.90   $1,334.00