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 $49.36   6.317%   $52.4781   $52.48   $52.50   $52.50  
  Purchase #2 $214.31   9.537%   $234.7487   $234.75   $234.75   $234.70  
  Purchase #3 $80.76   7.145%   $86.5303   $86.53   $86.55   $86.50  
  Purchase #4 $234.76   7.811%   $253.0971   $253.10   $253.10   $253.10  
  Purchase #5 $10.36   4.655%   $10.8423   $10.84   $10.85   $10.80  
  Purchase #6 $173.65   4.616%   $181.6657   $181.67   $181.65   $181.70  
  Purchase #7 $148.74   11.783%   $166.266   $166.27   $166.25   $166.30  
  7 purchase totals = $911.94       $985.6282   $985.64   $985.65   $985.60