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 $60.70   11.545%   $67.7078   $67.71   $67.70   $67.70  
  Purchase #2 $214.92   11.264%   $239.1286   $239.13   $239.15   $239.10  
  Purchase #3 $22.51   10.456%   $24.8636   $24.86   $24.85   $24.90  
  Purchase #4 $206.56   10.204%   $227.6374   $227.64   $227.65   $227.60  
  Purchase #5 $152.73   6.846%   $163.1859   $163.19   $163.20   $163.20  
  Purchase #6 $110.87   3.182%   $114.3979   $114.40   $114.40   $114.40  
  Purchase #7 $161.32   10.196%   $177.7682   $177.77   $177.75   $177.80  
  7 purchase totals = $929.61       $1,014.6894   $1,014.70   $1,014.70   $1,014.70