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 $208.45   9.123%   $227.4669   $227.47   $227.45   $227.50  
  Purchase #2 $244.61   13.373%   $277.3217   $277.32   $277.30   $277.30  
  Purchase #3 $154.88   12.721%   $174.5823   $174.58   $174.60   $174.60  
  Purchase #4 $108.32   11.505%   $120.7822   $120.78   $120.80   $120.80  
  Purchase #5 $236.71   10.832%   $262.3504   $262.35   $262.35   $262.40  
  Purchase #6 $67.56   11.528%   $75.3483   $75.35   $75.35   $75.30  
  Purchase #7 $83.35   3.148%   $85.9739   $85.97   $85.95   $86.00  
  7 purchase totals = $1,103.88       $1,223.8257   $1,223.82   $1,223.80   $1,223.90