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 $69.54   9.157%   $75.9078   $75.91   $75.90   $75.90  
  Purchase #2 $234.42   4.443%   $244.8353   $244.84   $244.85   $244.80  
  Purchase #3 $200.67   9.268%   $219.2681   $219.27   $219.25   $219.30  
  Purchase #4 $71.36   7.429%   $76.6613   $76.66   $76.65   $76.70  
  Purchase #5 $202.61   9.550%   $221.9593   $221.96   $221.95   $222.00  
  Purchase #6 $216.99   5.500%   $228.9245   $228.92   $228.90   $228.90  
  Purchase #7 $236.49   8.255%   $256.0122   $256.01   $256.00   $256.00  
  7 purchase totals = $1,232.08       $1,323.5685   $1,323.57   $1,323.50   $1,323.60