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 $56.64   7.595%   $60.9418   $60.94   $60.95   $60.90  
  Purchase #2 $185.62   9.377%   $203.0256   $203.03   $203.05   $203.00  
  Purchase #3 $61.65   5.446%   $65.0075   $65.01   $65.00   $65.00  
  Purchase #4 $228.51   10.528%   $252.5675   $252.57   $252.55   $252.60  
  Purchase #5 $10.45   11.460%   $11.6476   $11.65   $11.65   $11.60  
  Purchase #6 $124.32   8.333%   $134.6796   $134.68   $134.70   $134.70  
  Purchase #7 $143.46   11.386%   $159.7944   $159.79   $159.80   $159.80  
  7 purchase totals = $810.65       $887.6640   $887.67   $887.70   $887.60