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 $63.47   5.862%   $67.1906   $67.19   $67.20   $67.20  
  Purchase #2 $84.91   8.302%   $91.9592   $91.96   $91.95   $92.00  
  Purchase #3 $73.37   7.746%   $79.0532   $79.05   $79.05   $79.10  
  Purchase #4 $111.53   5.591%   $117.7656   $117.77   $117.75   $117.80  
  Purchase #5 $160.38   3.138%   $165.4127   $165.41   $165.40   $165.40  
  Purchase #6 $38.49   11.132%   $42.7747   $42.77   $42.75   $42.80  
  Purchase #7 $169.46   10.582%   $187.3923   $187.39   $187.40   $187.40  
  7 purchase totals = $701.61       $751.5483   $751.54   $751.50   $751.70