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 $62.41   11.241%   $69.4255   $69.43   $69.45   $69.40  
  Purchase #2 $86.65   3.469%   $89.6559   $89.66   $89.65   $89.70  
  Purchase #3 $176.65   12.191%   $198.1854   $198.19   $198.20   $198.20  
  Purchase #4 $156.87   13.405%   $177.8984   $177.90   $177.90   $177.90  
  Purchase #5 $25.85   8.606%   $28.0747   $28.07   $28.05   $28.10  
  Purchase #6 $208.95   4.123%   $217.565   $217.57   $217.55   $217.60  
  Purchase #7 $237.49   13.294%   $269.0619   $269.06   $269.05   $269.10  
  7 purchase totals = $954.87       $1,049.8668   $1,049.88   $1,049.85   $1,050.00