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 $60.39   5.422%   $63.6643   $63.66   $63.65   $63.70  
  Purchase #2 $95.54   6.403%   $101.6574   $101.66   $101.65   $101.70  
  Purchase #3 $55.33   8.767%   $60.1808   $60.18   $60.20   $60.20  
  Purchase #4 $162.44   9.556%   $177.9628   $177.96   $177.95   $178.00  
  Purchase #5 $94.75   3.638%   $98.197   $98.20   $98.20   $98.20  
  Purchase #6 $232.87   6.421%   $247.8226   $247.82   $247.80   $247.80  
  Purchase #7 $27.88   7.330%   $29.9236   $29.92   $29.90   $29.90  
  7 purchase totals = $729.20       $779.4085   $779.40   $779.35   $779.50