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 $84.28   4.469%   $88.0465   $88.05   $88.05   $88.00  
  Purchase #2 $131.73   13.322%   $149.2791   $149.28   $149.30   $149.30  
  Purchase #3 $175.28   7.353%   $188.1683   $188.17   $188.15   $188.20  
  Purchase #4 $210.45   7.818%   $226.903   $226.90   $226.90   $226.90  
  Purchase #5 $159.87   3.852%   $166.0282   $166.03   $166.05   $166.00  
  Purchase #6 $52.37   10.787%   $58.0192   $58.02   $58.00   $58.00  
  Purchase #7 $150.95   9.190%   $164.8223   $164.82   $164.80   $164.80  
  7 purchase totals = $964.93       $1,041.2666   $1,041.27   $1,041.25   $1,041.20