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 $177.83   9.677%   $195.0386   $195.04   $195.05   $195.00  
  Purchase #2 $116.68   5.391%   $122.9702   $122.97   $122.95   $123.00  
  Purchase #3 $56.25   12.716%   $63.4028   $63.40   $63.40   $63.40  
  Purchase #4 $120.57   6.166%   $128.0043   $128.00   $128.00   $128.00  
  Purchase #5 $217.64   13.576%   $247.1868   $247.19   $247.20   $247.20  
  Purchase #6 $58.84   4.504%   $61.4902   $61.49   $61.50   $61.50  
  Purchase #7 $34.27   13.588%   $38.9266   $38.93   $38.95   $38.90  
  7 purchase totals = $782.08       $857.0195   $857.02   $857.05   $857.00