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 $220.48   8.616%   $239.4766   $239.48   $239.50   $239.50  
  Purchase #2 $209.61   6.356%   $222.9328   $222.93   $222.95   $222.90  
  Purchase #3 $54.71   7.287%   $58.6967   $58.70   $58.70   $58.70  
  Purchase #4 $161.73   11.744%   $180.7236   $180.72   $180.70   $180.70  
  Purchase #5 $179.73   13.696%   $204.3458   $204.35   $204.35   $204.30  
  Purchase #6 $240.80   10.215%   $265.3977   $265.40   $265.40   $265.40  
  Purchase #7 $22.36   7.482%   $24.033   $24.03   $24.05   $24.00  
  7 purchase totals = $1,089.42       $1,195.6062   $1,195.61   $1,195.65   $1,195.50