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 $195.72   5.858%   $207.1853   $207.19   $207.20   $207.20  
  Purchase #2 $62.48   8.284%   $67.6558   $67.66   $67.65   $67.70  
  Purchase #3 $95.83   13.495%   $108.7623   $108.76   $108.75   $108.80  
  Purchase #4 $240.44   7.495%   $258.461   $258.46   $258.45   $258.50  
  Purchase #5 $71.50   13.175%   $80.9201   $80.92   $80.90   $80.90  
  Purchase #6 $39.89   3.222%   $41.1753   $41.18   $41.20   $41.20  
  Purchase #7 $177.87   3.542%   $184.1702   $184.17   $184.15   $184.20  
  7 purchase totals = $883.73       $948.3300   $948.34   $948.30   $948.50