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 $146.63   5.510%   $154.7093   $154.71   $154.70   $154.70  
  Purchase #2 $176.28   11.352%   $196.2913   $196.29   $196.30   $196.30  
  Purchase #3 $20.28   8.841%   $22.073   $22.07   $22.05   $22.10  
  Purchase #4 $62.55   7.246%   $67.0824   $67.08   $67.10   $67.10  
  Purchase #5 $72.53   9.825%   $79.6561   $79.66   $79.65   $79.70  
  Purchase #6 $184.54   4.830%   $193.4533   $193.45   $193.45   $193.50  
  Purchase #7 $245.68   5.794%   $259.9147   $259.91   $259.90   $259.90  
  7 purchase totals = $908.49       $973.1801   $973.17   $973.15   $973.30