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 $234.83   9.522%   $257.1905   $257.19   $257.20   $257.20  
  Purchase #2 $55.74   7.835%   $60.1072   $60.11   $60.10   $60.10  
  Purchase #3 $66.84   6.582%   $71.2394   $71.24   $71.25   $71.20  
  Purchase #4 $150.35   9.452%   $164.5611   $164.56   $164.55   $164.60  
  Purchase #5 $219.75   4.203%   $228.9861   $228.99   $229.00   $229.00  
  Purchase #6 $224.29   11.310%   $249.6572   $249.66   $249.65   $249.70  
  Purchase #7 $233.88   8.499%   $253.7575   $253.76   $253.75   $253.80  
  7 purchase totals = $1,185.68       $1,285.4990   $1,285.51   $1,285.50   $1,285.60