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 $213.63   10.859%   $236.8281   $236.83   $236.85   $236.80  
  Purchase #2 $169.88   13.282%   $192.4435   $192.44   $192.45   $192.40  
  Purchase #3 $144.47   6.287%   $153.5528   $153.55   $153.55   $153.60  
  Purchase #4 $236.70   3.463%   $244.8969   $244.90   $244.90   $244.90  
  Purchase #5 $157.38   5.409%   $165.8927   $165.89   $165.90   $165.90  
  Purchase #6 $170.31   12.360%   $191.3603   $191.36   $191.35   $191.40  
  Purchase #7 $40.82   12.600%   $45.9633   $45.96   $45.95   $46.00  
  7 purchase totals = $1,133.19       $1,230.9376   $1,230.93   $1,230.95   $1,231.00