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 $204.61   11.339%   $227.8107   $227.81   $227.80   $227.80  
  Purchase #2 $194.87   3.498%   $201.6866   $201.69   $201.70   $201.70  
  Purchase #3 $140.61   6.119%   $149.2139   $149.21   $149.20   $149.20  
  Purchase #4 $91.82   8.538%   $99.6596   $99.66   $99.65   $99.70  
  Purchase #5 $167.90   11.156%   $186.6309   $186.63   $186.65   $186.60  
  Purchase #6 $211.41   3.608%   $219.0377   $219.04   $219.05   $219.00  
  Purchase #7 $122.51   10.372%   $135.2167   $135.22   $135.20   $135.20  
  7 purchase totals = $1,133.73       $1,219.2561   $1,219.26   $1,219.25   $1,219.20