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 $151.99   11.691%   $169.7592   $169.76   $169.75   $169.80  
  Purchase #2 $114.91   11.753%   $128.4154   $128.42   $128.40   $128.40  
  Purchase #3 $43.70   4.668%   $45.7399   $45.74   $45.75   $45.70  
  Purchase #4 $211.49   10.307%   $233.2883   $233.29   $233.30   $233.30  
  Purchase #5 $126.92   11.803%   $141.9004   $141.90   $141.90   $141.90  
  Purchase #6 $19.74   4.367%   $20.602   $20.60   $20.60   $20.60  
  Purchase #7 $194.86   13.191%   $220.564   $220.56   $220.55   $220.60  
  7 purchase totals = $863.61       $960.2692   $960.27   $960.25   $960.30