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 $246.49   8.324%   $267.0078   $267.01   $267.00   $267.00  
  Purchase #2 $153.63   13.871%   $174.94   $174.94   $174.95   $174.90  
  Purchase #3 $182.31   5.651%   $192.6123   $192.61   $192.60   $192.60  
  Purchase #4 $194.96   11.690%   $217.7508   $217.75   $217.75   $217.80  
  Purchase #5 $226.85   5.861%   $240.1457   $240.15   $240.15   $240.10  
  Purchase #6 $232.98   11.216%   $259.111   $259.11   $259.10   $259.10  
  Purchase #7 $95.25   10.529%   $105.2789   $105.28   $105.30   $105.30  
  7 purchase totals = $1,332.47       $1,456.8465   $1,456.85   $1,456.85   $1,456.80