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 $172.88   3.776%   $179.4079   $179.41   $179.40   $179.40  
  Purchase #2 $141.25   10.868%   $156.6011   $156.60   $156.60   $156.60  
  Purchase #3 $71.94   3.189%   $74.2342   $74.23   $74.25   $74.20  
  Purchase #4 $21.44   7.700%   $23.0909   $23.09   $23.10   $23.10  
  Purchase #5 $143.78   13.359%   $162.9876   $162.99   $163.00   $163.00  
  Purchase #6 $188.68   6.486%   $200.9178   $200.92   $200.90   $200.90  
  Purchase #7 $39.31   12.123%   $44.0756   $44.08   $44.10   $44.10  
  7 purchase totals = $779.28       $841.3151   $841.32   $841.35   $841.30