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 $203.33   10.196%   $224.0615   $224.06   $224.05   $224.10  
  Purchase #2 $28.35   6.871%   $30.2979   $30.30   $30.30   $30.30  
  Purchase #3 $60.85   8.841%   $66.2297   $66.23   $66.25   $66.20  
  Purchase #4 $22.57   7.112%   $24.1752   $24.18   $24.20   $24.20  
  Purchase #5 $224.35   3.427%   $232.0385   $232.04   $232.05   $232.00  
  Purchase #6 $151.66   13.791%   $172.5754   $172.58   $172.60   $172.60  
  Purchase #7 $62.58   6.696%   $66.7704   $66.77   $66.75   $66.80  
  7 purchase totals = $753.69       $816.1486   $816.16   $816.20   $816.20