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 $68.65   7.373%   $73.7116   $73.71   $73.70   $73.70  
  Purchase #2 $244.67   10.505%   $270.3726   $270.37   $270.35   $270.40  
  Purchase #3 $98.49   13.304%   $111.5931   $111.59   $111.60   $111.60  
  Purchase #4 $231.83   6.119%   $246.0157   $246.02   $246.00   $246.00  
  Purchase #5 $190.94   4.460%   $199.4559   $199.46   $199.45   $199.50  
  Purchase #6 $10.31   11.834%   $11.5301   $11.53   $11.55   $11.50  
  Purchase #7 $36.69   6.165%   $38.9519   $38.95   $38.95   $39.00  
  7 purchase totals = $881.58       $951.6309   $951.63   $951.60   $951.70