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 $122.90   6.812%   $131.2719   $131.27   $131.25   $131.30  
  Purchase #2 $133.38   12.733%   $150.3633   $150.36   $150.35   $150.40  
  Purchase #3 $18.42   3.690%   $19.0997   $19.10   $19.10   $19.10  
  Purchase #4 $242.44   9.691%   $265.9349   $265.93   $265.95   $265.90  
  Purchase #5 $60.83   3.560%   $62.9955   $63.00   $63.00   $63.00  
  Purchase #6 $233.60   4.376%   $243.8223   $243.82   $243.80   $243.80  
  Purchase #7 $132.51   6.612%   $141.2716   $141.27   $141.25   $141.30  
  7 purchase totals = $944.08       $1,014.7592   $1,014.75   $1,014.70   $1,014.80