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 $125.73   8.745%   $136.7251   $136.73   $136.75   $136.70  
  Purchase #2 $157.73   8.813%   $171.6307   $171.63   $171.65   $171.60  
  Purchase #3 $70.63   11.808%   $78.97   $78.97   $78.95   $79.00  
  Purchase #4 $226.34   9.396%   $247.6069   $247.61   $247.60   $247.60  
  Purchase #5 $214.39   13.461%   $243.249   $243.25   $243.25   $243.20  
  Purchase #6 $211.28   13.272%   $239.3211   $239.32   $239.30   $239.30  
  Purchase #7 $145.75   4.568%   $152.4079   $152.41   $152.40   $152.40  
  7 purchase totals = $1,151.85       $1,269.9107   $1,269.92   $1,269.90   $1,269.80