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 $163.39   12.743%   $184.2108   $184.21   $184.20   $184.20  
  Purchase #2 $218.56   13.635%   $248.3607   $248.36   $248.35   $248.40  
  Purchase #3 $210.65   5.697%   $222.6507   $222.65   $222.65   $222.70  
  Purchase #4 $47.61   5.395%   $50.1786   $50.18   $50.20   $50.20  
  Purchase #5 $85.61   11.345%   $95.3225   $95.32   $95.30   $95.30  
  Purchase #6 $148.34   3.604%   $153.6862   $153.69   $153.70   $153.70  
  Purchase #7 $36.86   10.416%   $40.6993   $40.70   $40.70   $40.70  
  7 purchase totals = $911.02       $995.1088   $995.11   $995.10   $995.20