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 $183.93   13.641%   $209.0199   $209.02   $209.00   $209.00  
  Purchase #2 $151.80   9.192%   $165.7535   $165.75   $165.75   $165.80  
  Purchase #3 $111.96   3.213%   $115.5573   $115.56   $115.55   $115.60  
  Purchase #4 $101.52   12.312%   $114.0191   $114.02   $114.00   $114.00  
  Purchase #5 $47.85   13.751%   $54.4299   $54.43   $54.45   $54.40  
  Purchase #6 $94.47   4.814%   $99.0178   $99.02   $99.00   $99.00  
  Purchase #7 $169.37   4.141%   $176.3836   $176.38   $176.40   $176.40  
  7 purchase totals = $860.90       $934.1811   $934.18   $934.15   $934.20