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 $208.32   9.366%   $227.8313   $227.83   $227.85   $227.80  
  Purchase #2 $233.52   12.210%   $262.0328   $262.03   $262.05   $262.00  
  Purchase #3 $39.34   5.192%   $41.3825   $41.38   $41.40   $41.40  
  Purchase #4 $110.92   10.480%   $122.5444   $122.54   $122.55   $122.50  
  Purchase #5 $183.86   10.750%   $203.625   $203.63   $203.65   $203.60  
  Purchase #6 $158.30   11.814%   $177.0016   $177.00   $177.00   $177.00  
  Purchase #7 $164.63   9.332%   $179.9933   $179.99   $180.00   $180.00  
  7 purchase totals = $1,098.89       $1,214.4109   $1,214.40   $1,214.50   $1,214.30