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 $164.63   13.788%   $187.3292   $187.33   $187.35   $187.30  
  Purchase #2 $232.45   7.236%   $249.2701   $249.27   $249.25   $249.30  
  Purchase #3 $210.49   4.752%   $220.4925   $220.49   $220.50   $220.50  
  Purchase #4 $51.62   10.126%   $56.847   $56.85   $56.85   $56.80  
  Purchase #5 $160.82   13.658%   $182.7848   $182.78   $182.80   $182.80  
  Purchase #6 $120.77   5.463%   $127.3677   $127.37   $127.35   $127.40  
  Purchase #7 $9.98   6.559%   $10.6346   $10.63   $10.65   $10.60  
  7 purchase totals = $950.76       $1,034.7259   $1,034.72   $1,034.75   $1,034.70