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 $237.54   13.492%   $269.5889   $269.59   $269.60   $269.60  
  Purchase #2 $48.28   4.708%   $50.553   $50.55   $50.55   $50.60  
  Purchase #3 $26.41   10.344%   $29.1419   $29.14   $29.15   $29.10  
  Purchase #4 $142.74   10.168%   $157.2538   $157.25   $157.25   $157.30  
  Purchase #5 $195.93   13.650%   $222.6744   $222.67   $222.65   $222.70  
  Purchase #6 $108.34   9.838%   $118.9985   $119.00   $119.00   $119.00  
  Purchase #7 $191.31   4.218%   $199.3795   $199.38   $199.40   $199.40  
  7 purchase totals = $950.55       $1,047.5900   $1,047.58   $1,047.60   $1,047.70