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 $88.65   7.211%   $95.0426   $95.04   $95.05   $95.00  
  Purchase #2 $17.67   5.690%   $18.6754   $18.68   $18.70   $18.70  
  Purchase #3 $46.98   8.734%   $51.0832   $51.08   $51.10   $51.10  
  Purchase #4 $162.61   3.628%   $168.5095   $168.51   $168.50   $168.50  
  Purchase #5 $226.71   8.632%   $246.2796   $246.28   $246.30   $246.30  
  Purchase #6 $112.73   13.705%   $128.1796   $128.18   $128.20   $128.20  
  Purchase #7 $63.67   9.421%   $69.6684   $69.67   $69.65   $69.70  
  7 purchase totals = $719.02       $777.4383   $777.44   $777.50   $777.50