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 $69.98   9.355%   $76.5266   $76.53   $76.55   $76.50  
  Purchase #2 $89.59   10.436%   $98.9396   $98.94   $98.95   $98.90  
  Purchase #3 $66.86   12.121%   $74.9641   $74.96   $74.95   $75.00  
  Purchase #4 $229.48   13.305%   $260.0123   $260.01   $260.00   $260.00  
  Purchase #5 $163.95   7.482%   $176.2167   $176.22   $176.20   $176.20  
  Purchase #6 $197.81   11.180%   $219.9252   $219.93   $219.95   $219.90  
  Purchase #7 $81.44   4.306%   $84.9468   $84.95   $84.95   $84.90  
  7 purchase totals = $899.11       $991.5313   $991.54   $991.55   $991.40