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 $144.93   7.118%   $155.2461   $155.25   $155.25   $155.20  
  Purchase #2 $241.98   11.388%   $269.5367   $269.54   $269.55   $269.50  
  Purchase #3 $111.65   9.537%   $122.2981   $122.30   $122.30   $122.30  
  Purchase #4 $153.78   5.526%   $162.2779   $162.28   $162.30   $162.30  
  Purchase #5 $147.68   9.157%   $161.2031   $161.20   $161.20   $161.20  
  Purchase #6 $173.85   7.438%   $186.781   $186.78   $186.80   $186.80  
  Purchase #7 $7.59   4.293%   $7.9158   $7.92   $7.90   $7.90  
  7 purchase totals = $981.46       $1,065.2587   $1,065.27   $1,065.30   $1,065.20