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 $67.57   3.148%   $69.6971   $69.70   $69.70   $69.70  
  Purchase #2 $108.66   10.223%   $119.7683   $119.77   $119.75   $119.80  
  Purchase #3 $235.75   11.121%   $261.9678   $261.97   $261.95   $262.00  
  Purchase #4 $27.50   11.257%   $30.5957   $30.60   $30.60   $30.60  
  Purchase #5 $34.53   12.838%   $38.963   $38.96   $38.95   $39.00  
  Purchase #6 $49.58   8.560%   $53.824   $53.82   $53.80   $53.80  
  Purchase #7 $65.94   4.563%   $68.9488   $68.95   $68.95   $68.90  
  7 purchase totals = $589.53       $643.7647   $643.77   $643.70   $643.80