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 $91.47   13.260%   $103.5989   $103.60   $103.60   $103.60  
  Purchase #2 $239.42   12.175%   $268.5694   $268.57   $268.55   $268.60  
  Purchase #3 $153.88   12.219%   $172.6826   $172.68   $172.70   $172.70  
  Purchase #4 $123.69   9.831%   $135.85   $135.85   $135.85   $135.90  
  Purchase #5 $184.91   6.790%   $197.4654   $197.47   $197.45   $197.50  
  Purchase #6 $53.72   6.212%   $57.0571   $57.06   $57.05   $57.10  
  Purchase #7 $243.57   11.454%   $271.4685   $271.47   $271.45   $271.50  
  7 purchase totals = $1,090.66       $1,206.6919   $1,206.70   $1,206.65   $1,206.90