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 $97.48   7.699%   $104.985   $104.99   $105.00   $105.00  
  Purchase #2 $58.39   11.745%   $65.2479   $65.25   $65.25   $65.20  
  Purchase #3 $237.36   13.471%   $269.3348   $269.33   $269.35   $269.30  
  Purchase #4 $89.69   5.464%   $94.5907   $94.59   $94.60   $94.60  
  Purchase #5 $50.52   11.710%   $56.4359   $56.44   $56.45   $56.40  
  Purchase #6 $186.63   4.493%   $195.0153   $195.02   $195.00   $195.00  
  Purchase #7 $203.56   7.669%   $219.171   $219.17   $219.15   $219.20  
  7 purchase totals = $923.63       $1,004.7806   $1,004.79   $1,004.80   $1,004.70