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 $48.44   5.495%   $51.1018   $51.10   $51.10   $51.10  
  Purchase #2 $107.41   10.628%   $118.8255   $118.83   $118.85   $118.80  
  Purchase #3 $54.59   6.153%   $57.9489   $57.95   $57.95   $57.90  
  Purchase #4 $66.82   5.611%   $70.5693   $70.57   $70.55   $70.60  
  Purchase #5 $205.76   9.371%   $225.0418   $225.04   $225.05   $225.00  
  Purchase #6 $168.62   7.837%   $181.8347   $181.83   $181.85   $181.80  
  Purchase #7 $237.30   4.369%   $247.6676   $247.67   $247.65   $247.70  
  7 purchase totals = $888.94       $952.9896   $952.99   $953.00   $952.90