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 $165.38   8.835%   $179.9913   $179.99   $180.00   $180.00  
  Purchase #2 $197.87   8.438%   $214.5663   $214.57   $214.55   $214.60  
  Purchase #3 $28.49   6.561%   $30.3592   $30.36   $30.35   $30.40  
  Purchase #4 $144.47   12.456%   $162.4652   $162.47   $162.45   $162.50  
  Purchase #5 $28.43   4.389%   $29.6778   $29.68   $29.70   $29.70  
  Purchase #6 $40.28   11.464%   $44.8977   $44.90   $44.90   $44.90  
  Purchase #7 $203.60   7.320%   $218.5035   $218.50   $218.50   $218.50  
  7 purchase totals = $808.52       $880.4610   $880.47   $880.45   $880.60