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 $226.31   12.262%   $254.0601   $254.06   $254.05   $254.10  
  Purchase #2 $182.85   10.255%   $201.6013   $201.60   $201.60   $201.60  
  Purchase #3 $150.56   12.239%   $168.987   $168.99   $169.00   $169.00  
  Purchase #4 $233.66   12.355%   $262.5287   $262.53   $262.55   $262.50  
  Purchase #5 $77.42   12.358%   $86.9876   $86.99   $87.00   $87.00  
  Purchase #6 $27.99   8.416%   $30.3456   $30.35   $30.35   $30.30  
  Purchase #7 $235.82   13.271%   $267.1157   $267.12   $267.10   $267.10  
  7 purchase totals = $1,134.61       $1,271.6260   $1,271.64   $1,271.65   $1,271.60