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 $231.69   13.664%   $263.3481   $263.35   $263.35   $263.30  
  Purchase #2 $98.67   10.283%   $108.8162   $108.82   $108.80   $108.80  
  Purchase #3 $173.66   3.217%   $179.2466   $179.25   $179.25   $179.20  
  Purchase #4 $101.29   9.532%   $110.945   $110.95   $110.95   $110.90  
  Purchase #5 $220.78   5.390%   $232.68   $232.68   $232.70   $232.70  
  Purchase #6 $167.91   9.501%   $183.8631   $183.86   $183.85   $183.90  
  Purchase #7 $23.30   5.796%   $24.6505   $24.65   $24.65   $24.70  
  7 purchase totals = $1,017.30       $1,103.5495   $1,103.56   $1,103.55   $1,103.50