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 $220.41   9.529%   $241.4129   $241.41   $241.40   $241.40  
  Purchase #2 $34.44   11.651%   $38.4526   $38.45   $38.45   $38.50  
  Purchase #3 $18.33   5.793%   $19.3919   $19.39   $19.40   $19.40  
  Purchase #4 $203.56   6.767%   $217.3349   $217.33   $217.35   $217.30  
  Purchase #5 $168.67   3.574%   $174.6983   $174.70   $174.70   $174.70  
  Purchase #6 $116.51   5.303%   $122.6885   $122.69   $122.70   $122.70  
  Purchase #7 $189.26   5.805%   $200.2465   $200.25   $200.25   $200.20  
  7 purchase totals = $951.18       $1,014.2256   $1,014.22   $1,014.25   $1,014.20