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 $90.87   6.367%   $96.6557   $96.66   $96.65   $96.70  
  Purchase #2 $163.94   12.560%   $184.5309   $184.53   $184.55   $184.50  
  Purchase #3 $154.55   9.794%   $169.6866   $169.69   $169.70   $169.70  
  Purchase #4 $237.46   11.691%   $265.2214   $265.22   $265.20   $265.20  
  Purchase #5 $89.70   6.122%   $95.1914   $95.19   $95.20   $95.20  
  Purchase #6 $69.27   5.405%   $73.014   $73.01   $73.00   $73.00  
  Purchase #7 $101.93   12.202%   $114.3675   $114.37   $114.35   $114.40  
  7 purchase totals = $907.72       $998.6675   $998.67   $998.65   $998.70