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 $208.85   7.221%   $223.9311   $223.93   $223.95   $223.90  
  Purchase #2 $99.88   4.793%   $104.6672   $104.67   $104.65   $104.70  
  Purchase #3 $11.89   9.356%   $13.0024   $13.00   $13.00   $13.00  
  Purchase #4 $100.85   4.665%   $105.5547   $105.55   $105.55   $105.60  
  Purchase #5 $32.63   4.220%   $34.007   $34.01   $34.00   $34.00  
  Purchase #6 $23.82   6.133%   $25.2809   $25.28   $25.30   $25.30  
  Purchase #7 $154.95   13.843%   $176.3997   $176.40   $176.40   $176.40  
  7 purchase totals = $632.87       $682.8430   $682.84   $682.85   $682.90