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 $68.28   7.126%   $73.1456   $73.15   $73.15   $73.10  
  Purchase #2 $67.95   11.399%   $75.6956   $75.70   $75.70   $75.70  
  Purchase #3 $160.87   12.225%   $180.5364   $180.54   $180.55   $180.50  
  Purchase #4 $95.33   4.772%   $99.8791   $99.88   $99.90   $99.90  
  Purchase #5 $164.40   7.133%   $176.1267   $176.13   $176.15   $176.10  
  Purchase #6 $211.71   10.444%   $233.821   $233.82   $233.80   $233.80  
  Purchase #7 $43.74   4.360%   $45.6471   $45.65   $45.65   $45.60  
  7 purchase totals = $812.28       $884.8515   $884.87   $884.90   $884.70