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 $208.84   12.558%   $235.0661   $235.07   $235.05   $235.10  
  Purchase #2 $164.48   9.248%   $179.6911   $179.69   $179.70   $179.70  
  Purchase #3 $56.70   10.378%   $62.5843   $62.58   $62.60   $62.60  
  Purchase #4 $96.41   4.111%   $100.3734   $100.37   $100.35   $100.40  
  Purchase #5 $128.26   5.437%   $135.2335   $135.23   $135.25   $135.20  
  Purchase #6 $24.99   4.163%   $26.0303   $26.03   $26.05   $26.00  
  Purchase #7 $160.68   3.347%   $166.058   $166.06   $166.05   $166.10  
  7 purchase totals = $840.36       $905.0367   $905.03   $905.05   $905.10