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 $67.26   8.177%   $72.7599   $72.76   $72.75   $72.80  
  Purchase #2 $198.66   12.653%   $223.7964   $223.80   $223.80   $223.80  
  Purchase #3 $169.49   4.344%   $176.8526   $176.85   $176.85   $176.90  
  Purchase #4 $123.49   3.143%   $127.3713   $127.37   $127.35   $127.40  
  Purchase #5 $177.72   4.403%   $185.545   $185.55   $185.55   $185.50  
  Purchase #6 $189.95   11.710%   $212.1931   $212.19   $212.20   $212.20  
  Purchase #7 $211.29   13.447%   $239.7022   $239.70   $239.70   $239.70  
  7 purchase totals = $1,137.86       $1,238.2205   $1,238.22   $1,238.20   $1,238.30