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 $229.62   9.279%   $250.9264   $250.93   $250.95   $250.90  
  Purchase #2 $168.32   9.424%   $184.1825   $184.18   $184.20   $184.20  
  Purchase #3 $176.95   11.260%   $196.8746   $196.87   $196.85   $196.90  
  Purchase #4 $144.65   12.729%   $163.0625   $163.06   $163.05   $163.10  
  Purchase #5 $61.53   5.692%   $65.0323   $65.03   $65.05   $65.00  
  Purchase #6 $65.53   11.388%   $72.9926   $72.99   $73.00   $73.00  
  Purchase #7 $16.69   13.213%   $18.8952   $18.90   $18.90   $18.90  
  7 purchase totals = $863.29       $951.9661   $951.96   $952.00   $952.00