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 $149.63   9.743%   $164.2085   $164.21   $164.20   $164.20  
  Purchase #2 $34.62   4.324%   $36.117   $36.12   $36.10   $36.10  
  Purchase #3 $214.54   9.432%   $234.7754   $234.78   $234.80   $234.80  
  Purchase #4 $35.84   3.819%   $37.2087   $37.21   $37.20   $37.20  
  Purchase #5 $58.99   11.802%   $65.952   $65.95   $65.95   $66.00  
  Purchase #6 $200.56   9.739%   $220.0925   $220.09   $220.10   $220.10  
  Purchase #7 $230.99   6.534%   $246.0829   $246.08   $246.10   $246.10  
  7 purchase totals = $925.17       $1,004.4370   $1,004.44   $1,004.45   $1,004.50