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 $57.47   13.255%   $65.0876   $65.09   $65.10   $65.10  
  Purchase #2 $177.34   13.339%   $200.9954   $201.00   $201.00   $201.00  
  Purchase #3 $125.99   8.351%   $136.5114   $136.51   $136.50   $136.50  
  Purchase #4 $168.64   3.255%   $174.1292   $174.13   $174.15   $174.10  
  Purchase #5 $185.32   11.705%   $207.0117   $207.01   $207.00   $207.00  
  Purchase #6 $195.73   3.391%   $202.3672   $202.37   $202.35   $202.40  
  Purchase #7 $141.92   4.162%   $147.8267   $147.83   $147.85   $147.80  
  7 purchase totals = $1,052.41       $1,133.9292   $1,133.94   $1,133.95   $1,133.90