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 $172.60   12.245%   $193.7349   $193.73   $193.75   $193.70  
  Purchase #2 $41.68   13.702%   $47.391   $47.39   $47.40   $47.40  
  Purchase #3 $117.28   8.792%   $127.5913   $127.59   $127.60   $127.60  
  Purchase #4 $159.91   4.187%   $166.6054   $166.61   $166.60   $166.60  
  Purchase #5 $158.33   8.346%   $171.5442   $171.54   $171.55   $171.50  
  Purchase #6 $108.32   6.552%   $115.4171   $115.42   $115.40   $115.40  
  Purchase #7 $184.28   9.196%   $201.2264   $201.23   $201.25   $201.20  
  7 purchase totals = $942.40       $1,023.5103   $1,023.51   $1,023.55   $1,023.40