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 $68.62   11.216%   $76.3164   $76.32   $76.30   $76.30  
  Purchase #2 $165.75   10.859%   $183.7488   $183.75   $183.75   $183.70  
  Purchase #3 $68.44   5.222%   $72.0139   $72.01   $72.00   $72.00  
  Purchase #4 $206.58   9.275%   $225.7403   $225.74   $225.75   $225.70  
  Purchase #5 $123.30   4.242%   $128.5304   $128.53   $128.55   $128.50  
  Purchase #6 $14.68   13.616%   $16.6788   $16.68   $16.70   $16.70  
  Purchase #7 $6.74   11.533%   $7.5173   $7.52   $7.50   $7.50  
  7 purchase totals = $654.11       $710.5459   $710.55   $710.55   $710.40