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 $183.35   12.719%   $206.6703   $206.67   $206.65   $206.70  
  Purchase #2 $16.84   6.147%   $17.8752   $17.88   $17.90   $17.90  
  Purchase #3 $116.64   5.455%   $123.0027   $123.00   $123.00   $123.00  
  Purchase #4 $62.97   4.528%   $65.8213   $65.82   $65.80   $65.80  
  Purchase #5 $147.90   4.355%   $154.341   $154.34   $154.35   $154.30  
  Purchase #6 $220.53   13.211%   $249.6642   $249.66   $249.65   $249.70  
  Purchase #7 $225.41   9.818%   $247.5408   $247.54   $247.55   $247.50  
  7 purchase totals = $973.64       $1,064.9155   $1,064.91   $1,064.90   $1,064.90