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 $82.31   11.778%   $92.0045   $92.00   $92.00   $92.00  
  Purchase #2 $6.89   4.501%   $7.2001   $7.20   $7.20   $7.20  
  Purchase #3 $47.50   4.668%   $49.7173   $49.72   $49.70   $49.70  
  Purchase #4 $88.88   9.521%   $97.3423   $97.34   $97.35   $97.30  
  Purchase #5 $228.34   13.135%   $258.3325   $258.33   $258.35   $258.30  
  Purchase #6 $92.53   4.761%   $96.9354   $96.94   $96.95   $96.90  
  Purchase #7 $205.48   9.343%   $224.678   $224.68   $224.70   $224.70  
  7 purchase totals = $751.93       $826.2101   $826.21   $826.25   $826.10