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 $237.77   13.250%   $269.2745   $269.27   $269.25   $269.30  
  Purchase #2 $165.25   8.816%   $179.8184   $179.82   $179.80   $179.80  
  Purchase #3 $126.49   8.262%   $136.9406   $136.94   $136.95   $136.90  
  Purchase #4 $80.97   9.407%   $88.5868   $88.59   $88.60   $88.60  
  Purchase #5 $178.32   9.334%   $194.9644   $194.96   $194.95   $195.00  
  Purchase #6 $93.70   3.446%   $96.9289   $96.93   $96.95   $96.90  
  Purchase #7 $204.37   4.752%   $214.0817   $214.08   $214.10   $214.10  
  7 purchase totals = $1,086.87       $1,180.5953   $1,180.59   $1,180.60   $1,180.60