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 $56.63   11.203%   $62.9743   $62.97   $62.95   $63.00  
  Purchase #2 $5.31   4.325%   $5.5397   $5.54   $5.55   $5.50  
  Purchase #3 $49.25   4.163%   $51.3003   $51.30   $51.30   $51.30  
  Purchase #4 $221.88   5.780%   $234.7047   $234.70   $234.70   $234.70  
  Purchase #5 $95.56   5.559%   $100.8722   $100.87   $100.85   $100.90  
  Purchase #6 $162.57   10.208%   $179.1651   $179.17   $179.15   $179.20  
  Purchase #7 $181.68   4.758%   $190.3243   $190.32   $190.30   $190.30  
  7 purchase totals = $772.88       $824.8806   $824.87   $824.80   $824.90