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 $241.52   8.363%   $261.7183   $261.72   $261.70   $261.70  
  Purchase #2 $33.25   9.118%   $36.2817   $36.28   $36.30   $36.30  
  Purchase #3 $57.40   11.199%   $63.8282   $63.83   $63.85   $63.80  
  Purchase #4 $171.31   5.738%   $181.1398   $181.14   $181.15   $181.10  
  Purchase #5 $50.83   13.782%   $57.8354   $57.84   $57.85   $57.80  
  Purchase #6 $160.90   3.131%   $165.9378   $165.94   $165.95   $165.90  
  Purchase #7 $110.26   5.422%   $116.2383   $116.24   $116.25   $116.20  
  7 purchase totals = $825.47       $882.9795   $882.99   $883.05   $882.80