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 $21.56   11.149%   $23.9637   $23.96   $23.95   $24.00  
  Purchase #2 $206.54   10.440%   $228.1028   $228.10   $228.10   $228.10  
  Purchase #3 $42.91   8.574%   $46.5891   $46.59   $46.60   $46.60  
  Purchase #4 $201.79   8.270%   $218.478   $218.48   $218.50   $218.50  
  Purchase #5 $82.37   10.553%   $91.0625   $91.06   $91.05   $91.10  
  Purchase #6 $57.92   6.349%   $61.5973   $61.60   $61.60   $61.60  
  Purchase #7 $81.65   9.417%   $89.339   $89.34   $89.35   $89.30  
  7 purchase totals = $694.74       $759.1324   $759.13   $759.15   $759.20