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 $91.74   4.855%   $96.194   $96.19   $96.20   $96.20  
  Purchase #2 $35.43   4.310%   $36.957   $36.96   $36.95   $37.00  
  Purchase #3 $147.38   11.727%   $164.6633   $164.66   $164.65   $164.70  
  Purchase #4 $134.34   10.166%   $147.997   $148.00   $148.00   $148.00  
  Purchase #5 $80.54   11.757%   $90.0091   $90.01   $90.00   $90.00  
  Purchase #6 $248.50   5.599%   $262.4135   $262.41   $262.40   $262.40  
  Purchase #7 $249.44   13.456%   $283.0046   $283.00   $283.00   $283.00  
  7 purchase totals = $987.37       $1,081.2385   $1,081.23   $1,081.20   $1,081.30