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 $25.66   7.538%   $27.5943   $27.59   $27.60   $27.60  
  Purchase #2 $183.38   8.578%   $199.1103   $199.11   $199.10   $199.10  
  Purchase #3 $113.32   8.255%   $122.6746   $122.67   $122.65   $122.70  
  Purchase #4 $133.44   12.305%   $149.8598   $149.86   $149.85   $149.90  
  Purchase #5 $188.64   13.806%   $214.6836   $214.68   $214.70   $214.70  
  Purchase #6 $128.50   3.165%   $132.567   $132.57   $132.55   $132.60  
  Purchase #7 $48.32   3.344%   $49.9358   $49.94   $49.95   $49.90  
  7 purchase totals = $821.26       $896.4254   $896.42   $896.40   $896.50