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 $130.27   13.419%   $147.7509   $147.75   $147.75   $147.80  
  Purchase #2 $24.33   6.494%   $25.91   $25.91   $25.90   $25.90  
  Purchase #3 $45.47   4.631%   $47.5757   $47.58   $47.60   $47.60  
  Purchase #4 $147.54   4.523%   $154.2132   $154.21   $154.20   $154.20  
  Purchase #5 $229.61   4.606%   $240.1858   $240.19   $240.20   $240.20  
  Purchase #6 $200.58   5.410%   $211.4314   $211.43   $211.45   $211.40  
  Purchase #7 $21.36   11.442%   $23.804   $23.80   $23.80   $23.80  
  7 purchase totals = $799.16       $850.8710   $850.87   $850.90   $850.90