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 $32.63   8.751%   $35.4855   $35.49   $35.50   $35.50  
  Purchase #2 $158.45   6.741%   $169.1311   $169.13   $169.15   $169.10  
  Purchase #3 $158.63   5.840%   $167.894   $167.89   $167.90   $167.90  
  Purchase #4 $119.88   4.155%   $124.861   $124.86   $124.85   $124.90  
  Purchase #5 $105.50   7.148%   $113.0411   $113.04   $113.05   $113.00  
  Purchase #6 $237.86   3.701%   $246.6632   $246.66   $246.65   $246.70  
  Purchase #7 $248.99   6.721%   $265.7246   $265.72   $265.70   $265.70  
  7 purchase totals = $1,061.94       $1,122.8005   $1,122.79   $1,122.80   $1,122.80