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 $57.63   9.413%   $63.0547   $63.05   $63.05   $63.10  
  Purchase #2 $163.98   7.816%   $176.7967   $176.80   $176.80   $176.80  
  Purchase #3 $92.51   7.621%   $99.5602   $99.56   $99.55   $99.60  
  Purchase #4 $21.34   12.724%   $24.0553   $24.06   $24.05   $24.10  
  Purchase #5 $218.98   12.661%   $246.7051   $246.71   $246.70   $246.70  
  Purchase #6 $186.58   5.744%   $197.2972   $197.30   $197.30   $197.30  
  Purchase #7 $24.27   10.762%   $26.8819   $26.88   $26.90   $26.90  
  7 purchase totals = $765.29       $834.3511   $834.36   $834.35   $834.50