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 $228.34   8.622%   $248.0275   $248.03   $248.05   $248.00  
  Purchase #2 $226.60   5.571%   $239.2239   $239.22   $239.20   $239.20  
  Purchase #3 $12.90   3.231%   $13.3168   $13.32   $13.30   $13.30  
  Purchase #4 $143.76   8.345%   $155.7568   $155.76   $155.75   $155.80  
  Purchase #5 $83.74   3.244%   $86.4565   $86.46   $86.45   $86.50  
  Purchase #6 $232.34   5.430%   $244.9561   $244.96   $244.95   $245.00  
  Purchase #7 $33.26   8.684%   $36.1483   $36.15   $36.15   $36.10  
  7 purchase totals = $960.94       $1,023.8859   $1,023.90   $1,023.85   $1,023.90