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 $94.42   8.730%   $102.6629   $102.66   $102.65   $102.70  
  Purchase #2 $67.28   11.597%   $75.0825   $75.08   $75.10   $75.10  
  Purchase #3 $170.49   12.143%   $191.1926   $191.19   $191.20   $191.20  
  Purchase #4 $106.26   9.724%   $116.5927   $116.59   $116.60   $116.60  
  Purchase #5 $245.74   8.458%   $266.5247   $266.52   $266.50   $266.50  
  Purchase #6 $60.28   9.126%   $65.7812   $65.78   $65.80   $65.80  
  Purchase #7 $5.90   7.695%   $6.354   $6.35   $6.35   $6.40  
  7 purchase totals = $750.37       $824.1906   $824.17   $824.20   $824.30