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 $245.46   9.587%   $268.9923   $268.99   $269.00   $269.00  
  Purchase #2 $164.92   12.351%   $185.2893   $185.29   $185.30   $185.30  
  Purchase #3 $9.68   12.816%   $10.9206   $10.92   $10.90   $10.90  
  Purchase #4 $87.33   7.775%   $94.1199   $94.12   $94.10   $94.10  
  Purchase #5 $164.49   8.732%   $178.8533   $178.85   $178.85   $178.90  
  Purchase #6 $238.92   6.229%   $253.8023   $253.80   $253.80   $253.80  
  Purchase #7 $75.99   5.283%   $80.0046   $80.00   $80.00   $80.00  
  7 purchase totals = $986.79       $1,071.9823   $1,071.97   $1,071.95   $1,072.00