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 $82.35   8.699%   $89.5136   $89.51   $89.50   $89.50  
  Purchase #2 $207.96   3.224%   $214.6646   $214.66   $214.65   $214.70  
  Purchase #3 $67.33   11.290%   $74.9316   $74.93   $74.95   $74.90  
  Purchase #4 $249.43   3.809%   $258.9308   $258.93   $258.95   $258.90  
  Purchase #5 $154.60   10.796%   $171.2906   $171.29   $171.30   $171.30  
  Purchase #6 $241.30   3.162%   $248.9299   $248.93   $248.95   $248.90  
  Purchase #7 $177.84   5.123%   $186.9507   $186.95   $186.95   $187.00  
  7 purchase totals = $1,180.81       $1,245.2118   $1,245.20   $1,245.25   $1,245.20