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 $177.53   10.695%   $196.5168   $196.52   $196.50   $196.50  
  Purchase #2 $189.51   6.156%   $201.1762   $201.18   $201.20   $201.20  
  Purchase #3 $59.88   10.115%   $65.9369   $65.94   $65.95   $65.90  
  Purchase #4 $150.94   11.325%   $168.034   $168.03   $168.05   $168.00  
  Purchase #5 $33.44   6.734%   $35.6918   $35.69   $35.70   $35.70  
  Purchase #6 $95.96   8.548%   $104.1627   $104.16   $104.15   $104.20  
  Purchase #7 $202.65   9.724%   $222.3557   $222.36   $222.35   $222.40  
  7 purchase totals = $909.91       $993.8741   $993.88   $993.90   $993.90