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 $159.86   13.123%   $180.8384   $180.84   $180.85   $180.80  
  Purchase #2 $59.36   13.713%   $67.5   $67.50   $67.50   $67.50  
  Purchase #3 $70.99   9.599%   $77.8043   $77.80   $77.80   $77.80  
  Purchase #4 $231.29   4.144%   $240.8747   $240.87   $240.85   $240.90  
  Purchase #5 $102.99   12.863%   $116.2376   $116.24   $116.25   $116.20  
  Purchase #6 $209.29   4.520%   $218.7499   $218.75   $218.75   $218.70  
  Purchase #7 $46.49   3.647%   $48.1855   $48.19   $48.20   $48.20  
  7 purchase totals = $880.27       $950.1904   $950.19   $950.20   $950.10