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 $216.94   11.202%   $241.2416   $241.24   $241.25   $241.20  
  Purchase #2 $143.47   6.345%   $152.5732   $152.57   $152.55   $152.60  
  Purchase #3 $160.77   9.241%   $175.6268   $175.63   $175.65   $175.60  
  Purchase #4 $42.96   7.221%   $46.0621   $46.06   $46.05   $46.10  
  Purchase #5 $24.87   3.151%   $25.6537   $25.65   $25.65   $25.70  
  Purchase #6 $52.77   10.870%   $58.5061   $58.51   $58.50   $58.50  
  Purchase #7 $236.45   11.409%   $263.4266   $263.43   $263.45   $263.40  
  7 purchase totals = $878.23       $963.0901   $963.09   $963.10   $963.10