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 $211.74   9.381%   $231.6033   $231.60   $231.60   $231.60  
  Purchase #2 $245.27   5.578%   $258.9512   $258.95   $258.95   $259.00  
  Purchase #3 $239.95   3.784%   $249.0297   $249.03   $249.05   $249.00  
  Purchase #4 $56.35   4.743%   $59.0227   $59.02   $59.00   $59.00  
  Purchase #5 $73.59   9.705%   $80.7319   $80.73   $80.75   $80.70  
  Purchase #6 $225.26   10.729%   $249.4281   $249.43   $249.45   $249.40  
  Purchase #7 $148.32   3.737%   $153.8627   $153.86   $153.85   $153.90  
  7 purchase totals = $1,200.48       $1,282.6296   $1,282.62   $1,282.65   $1,282.60