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 $68.74   7.311%   $73.7656   $73.77   $73.75   $73.80  
  Purchase #2 $222.44   11.106%   $247.1442   $247.14   $247.15   $247.10  
  Purchase #3 $215.55   13.565%   $244.7894   $244.79   $244.80   $244.80  
  Purchase #4 $215.87   9.581%   $236.5525   $236.55   $236.55   $236.60  
  Purchase #5 $122.92   6.206%   $130.5484   $130.55   $130.55   $130.50  
  Purchase #6 $137.93   10.126%   $151.8968   $151.90   $151.90   $151.90  
  Purchase #7 $129.99   10.795%   $144.0224   $144.02   $144.00   $144.00  
  7 purchase totals = $1,113.44       $1,228.7193   $1,228.72   $1,228.70   $1,228.70