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 $204.34   13.838%   $232.6166   $232.62   $232.60   $232.60  
  Purchase #2 $33.32   11.362%   $37.1058   $37.11   $37.10   $37.10  
  Purchase #3 $60.88   13.369%   $69.019   $69.02   $69.00   $69.00  
  Purchase #4 $214.94   11.187%   $238.9853   $238.99   $239.00   $239.00  
  Purchase #5 $83.62   7.773%   $90.1198   $90.12   $90.10   $90.10  
  Purchase #6 $86.67   8.515%   $94.05   $94.05   $94.05   $94.10  
  Purchase #7 $51.25   8.689%   $55.7031   $55.70   $55.70   $55.70  
  7 purchase totals = $735.02       $817.5996   $817.61   $817.55   $817.60