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 $200.98   6.821%   $214.6888   $214.69   $214.70   $214.70  
  Purchase #2 $153.88   3.399%   $159.1104   $159.11   $159.10   $159.10  
  Purchase #3 $73.33   11.142%   $81.5004   $81.50   $81.50   $81.50  
  Purchase #4 $38.67   11.518%   $43.124   $43.12   $43.10   $43.10  
  Purchase #5 $111.69   10.587%   $123.5146   $123.51   $123.50   $123.50  
  Purchase #6 $194.91   3.841%   $202.3965   $202.40   $202.40   $202.40  
  Purchase #7 $176.55   5.590%   $186.4191   $186.42   $186.40   $186.40  
  7 purchase totals = $950.01       $1,010.7538   $1,010.75   $1,010.70   $1,010.70