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 $196.84   6.151%   $208.9476   $208.95   $208.95   $208.90  
  Purchase #2 $157.53   12.146%   $176.6636   $176.66   $176.65   $176.70  
  Purchase #3 $235.93   6.824%   $252.0299   $252.03   $252.05   $252.00  
  Purchase #4 $234.89   10.191%   $258.8276   $258.83   $258.85   $258.80  
  Purchase #5 $123.94   3.262%   $127.9829   $127.98   $128.00   $128.00  
  Purchase #6 $178.52   11.825%   $199.63   $199.63   $199.65   $199.60  
  Purchase #7 $148.90   6.124%   $158.0186   $158.02   $158.00   $158.00  
  7 purchase totals = $1,276.55       $1,382.1002   $1,382.10   $1,382.15   $1,382.00