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 $76.45   13.382%   $86.6805   $86.68   $86.70   $86.70  
  Purchase #2 $169.74   12.473%   $190.9117   $190.91   $190.90   $190.90  
  Purchase #3 $149.70   6.681%   $159.7015   $159.70   $159.70   $159.70  
  Purchase #4 $202.81   6.818%   $216.6376   $216.64   $216.65   $216.60  
  Purchase #5 $130.51   11.399%   $145.3868   $145.39   $145.40   $145.40  
  Purchase #6 $239.41   9.665%   $262.549   $262.55   $262.55   $262.50  
  Purchase #7 $171.52   6.132%   $182.0376   $182.04   $182.05   $182.00  
  7 purchase totals = $1,140.14       $1,243.9047   $1,243.91   $1,243.95   $1,243.80