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 $68.82   7.604%   $74.0531   $74.05   $74.05   $74.10  
  Purchase #2 $126.28   4.508%   $131.9727   $131.97   $131.95   $132.00  
  Purchase #3 $127.94   6.772%   $136.6041   $136.60   $136.60   $136.60  
  Purchase #4 $202.67   7.790%   $218.458   $218.46   $218.45   $218.50  
  Purchase #5 $134.97   5.217%   $142.0114   $142.01   $142.00   $142.00  
  Purchase #6 $45.62   13.119%   $51.6049   $51.60   $51.60   $51.60  
  Purchase #7 $219.93   10.194%   $242.3497   $242.35   $242.35   $242.30  
  7 purchase totals = $926.23       $997.0539   $997.04   $997.00   $997.10