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 $196.26   3.753%   $203.6256   $203.63   $203.65   $203.60  
  Purchase #2 $248.69   9.787%   $273.0293   $273.03   $273.05   $273.00  
  Purchase #3 $8.73   9.160%   $9.5297   $9.53   $9.55   $9.50  
  Purchase #4 $86.64   5.870%   $91.7258   $91.73   $91.75   $91.70  
  Purchase #5 $137.99   5.137%   $145.0785   $145.08   $145.10   $145.10  
  Purchase #6 $222.70   9.271%   $243.3465   $243.35   $243.35   $243.30  
  Purchase #7 $15.78   5.242%   $16.6072   $16.61   $16.60   $16.60  
  7 purchase totals = $916.79       $982.9426   $982.96   $983.05   $982.80