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 $105.94   9.449%   $115.9503   $115.95   $115.95   $116.00  
  Purchase #2 $99.29   10.126%   $109.3441   $109.34   $109.35   $109.30  
  Purchase #3 $193.77   11.589%   $216.226   $216.23   $216.25   $216.20  
  Purchase #4 $162.57   10.717%   $179.9926   $179.99   $180.00   $180.00  
  Purchase #5 $125.30   12.237%   $140.633   $140.63   $140.65   $140.60  
  Purchase #6 $140.84   9.240%   $153.8536   $153.85   $153.85   $153.90  
  Purchase #7 $127.48   13.438%   $144.6108   $144.61   $144.60   $144.60  
  7 purchase totals = $955.19       $1,060.6104   $1,060.60   $1,060.65   $1,060.60