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 $73.65   3.752%   $76.4133   $76.41   $76.40   $76.40  
  Purchase #2 $165.59   5.397%   $174.5269   $174.53   $174.55   $174.50  
  Purchase #3 $161.57   12.301%   $181.4447   $181.44   $181.45   $181.40  
  Purchase #4 $194.99   11.609%   $217.6264   $217.63   $217.65   $217.60  
  Purchase #5 $211.32   13.622%   $240.106   $240.11   $240.10   $240.10  
  Purchase #6 $31.54   12.711%   $35.549   $35.55   $35.55   $35.50  
  Purchase #7 $176.91   13.504%   $200.7999   $200.80   $200.80   $200.80  
  7 purchase totals = $1,015.57       $1,126.4662   $1,126.47   $1,126.50   $1,126.30