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 $34.95   8.787%   $38.0211   $38.02   $38.00   $38.00  
  Purchase #2 $174.93   10.708%   $193.6615   $193.66   $193.65   $193.70  
  Purchase #3 $11.95   6.714%   $12.7523   $12.75   $12.75   $12.80  
  Purchase #4 $196.72   5.749%   $208.0294   $208.03   $208.05   $208.00  
  Purchase #5 $233.44   3.361%   $241.2859   $241.29   $241.30   $241.30  
  Purchase #6 $189.72   11.758%   $212.0273   $212.03   $212.05   $212.00  
  Purchase #7 $152.95   11.699%   $170.8436   $170.84   $170.85   $170.80  
  7 purchase totals = $994.66       $1,076.6211   $1,076.62   $1,076.65   $1,076.60