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 $188.93   4.111%   $196.6969   $196.70   $196.70   $196.70  
  Purchase #2 $50.30   11.674%   $56.172   $56.17   $56.15   $56.20  
  Purchase #3 $50.45   5.834%   $53.3933   $53.39   $53.40   $53.40  
  Purchase #4 $73.67   9.772%   $80.869   $80.87   $80.85   $80.90  
  Purchase #5 $157.79   13.782%   $179.5366   $179.54   $179.55   $179.50  
  Purchase #6 $42.37   6.140%   $44.9715   $44.97   $44.95   $45.00  
  Purchase #7 $109.91   3.715%   $113.9932   $113.99   $114.00   $114.00  
  7 purchase totals = $673.42       $725.6325   $725.63   $725.60   $725.70