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 $207.62   8.753%   $225.793   $225.79   $225.80   $225.80  
  Purchase #2 $250.99   10.138%   $276.4354   $276.44   $276.45   $276.40  
  Purchase #3 $76.40   13.767%   $86.918   $86.92   $86.90   $86.90  
  Purchase #4 $241.30   5.226%   $253.9103   $253.91   $253.90   $253.90  
  Purchase #5 $142.58   5.237%   $150.0469   $150.05   $150.05   $150.00  
  Purchase #6 $194.42   9.507%   $212.9035   $212.90   $212.90   $212.90  
  Purchase #7 $5.36   12.716%   $6.0416   $6.04   $6.05   $6.00  
  7 purchase totals = $1,118.67       $1,212.0487   $1,212.05   $1,212.05   $1,211.90