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 $215.91   7.534%   $232.1767   $232.18   $232.20   $232.20  
  Purchase #2 $140.36   9.646%   $153.8991   $153.90   $153.90   $153.90  
  Purchase #3 $23.56   11.353%   $26.2348   $26.23   $26.25   $26.20  
  Purchase #4 $241.39   13.723%   $274.5159   $274.52   $274.50   $274.50  
  Purchase #5 $18.39   8.115%   $19.8823   $19.88   $19.90   $19.90  
  Purchase #6 $66.49   6.488%   $70.8039   $70.80   $70.80   $70.80  
  Purchase #7 $159.27   11.770%   $178.0161   $178.02   $178.00   $178.00  
  7 purchase totals = $865.37       $955.5288   $955.53   $955.55   $955.50