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 $189.44   9.503%   $207.4425   $207.44   $207.45   $207.40  
  Purchase #2 $138.51   3.732%   $143.6792   $143.68   $143.70   $143.70  
  Purchase #3 $239.27   13.726%   $272.1122   $272.11   $272.10   $272.10  
  Purchase #4 $153.41   10.414%   $169.3861   $169.39   $169.40   $169.40  
  Purchase #5 $187.60   8.346%   $203.2571   $203.26   $203.25   $203.30  
  Purchase #6 $46.74   3.493%   $48.3726   $48.37   $48.35   $48.40  
  Purchase #7 $59.53   13.581%   $67.6148   $67.61   $67.60   $67.60  
  7 purchase totals = $1,014.50       $1,111.8645   $1,111.86   $1,111.85   $1,111.90