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 $203.42   11.226%   $226.2559   $226.26   $226.25   $226.30  
  Purchase #2 $79.63   5.415%   $83.942   $83.94   $83.95   $83.90  
  Purchase #3 $216.68   9.651%   $237.5918   $237.59   $237.60   $237.60  
  Purchase #4 $55.69   10.301%   $61.4266   $61.43   $61.45   $61.40  
  Purchase #5 $197.94   10.673%   $219.0661   $219.07   $219.05   $219.10  
  Purchase #6 $171.79   10.658%   $190.0994   $190.10   $190.10   $190.10  
  Purchase #7 $7.99   13.376%   $9.0587   $9.06   $9.05   $9.10  
  7 purchase totals = $933.14       $1,027.4405   $1,027.45   $1,027.45   $1,027.50