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 $166.76   6.708%   $177.9463   $177.95   $177.95   $177.90  
  Purchase #2 $194.41   13.257%   $220.1829   $220.18   $220.20   $220.20  
  Purchase #3 $34.55   11.611%   $38.5616   $38.56   $38.55   $38.60  
  Purchase #4 $241.25   13.289%   $273.3097   $273.31   $273.30   $273.30  
  Purchase #5 $152.77   5.646%   $161.3954   $161.40   $161.40   $161.40  
  Purchase #6 $188.40   7.302%   $202.157   $202.16   $202.15   $202.20  
  Purchase #7 $162.62   11.848%   $181.8872   $181.89   $181.90   $181.90  
  7 purchase totals = $1,140.76       $1,255.4401   $1,255.45   $1,255.45   $1,255.50