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 $191.76   8.328%   $207.7298   $207.73   $207.75   $207.70  
  Purchase #2 $159.71   10.109%   $175.8551   $175.86   $175.85   $175.90  
  Purchase #3 $232.54   8.723%   $252.8245   $252.82   $252.80   $252.80  
  Purchase #4 $57.89   8.864%   $63.0214   $63.02   $63.00   $63.00  
  Purchase #5 $94.31   9.801%   $103.5533   $103.55   $103.55   $103.60  
  Purchase #6 $41.93   4.663%   $43.8852   $43.89   $43.90   $43.90  
  Purchase #7 $242.68   13.645%   $275.7937   $275.79   $275.80   $275.80  
  7 purchase totals = $1,020.82       $1,122.6630   $1,122.66   $1,122.65   $1,122.70