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 $53.36   9.188%   $58.2627   $58.26   $58.25   $58.30  
  Purchase #2 $219.44   11.493%   $244.6602   $244.66   $244.65   $244.70  
  Purchase #3 $165.30   3.812%   $171.6012   $171.60   $171.60   $171.60  
  Purchase #4 $244.95   12.441%   $275.4242   $275.42   $275.40   $275.40  
  Purchase #5 $10.42   13.578%   $11.8348   $11.83   $11.85   $11.80  
  Purchase #6 $181.83   7.562%   $195.58   $195.58   $195.60   $195.60  
  Purchase #7 $175.69   9.478%   $192.3419   $192.34   $192.35   $192.30  
  7 purchase totals = $1,050.99       $1,149.7050   $1,149.69   $1,149.70   $1,149.70