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 $59.83   10.802%   $66.2928   $66.29   $66.30   $66.30  
  Purchase #2 $56.92   5.798%   $60.2202   $60.22   $60.20   $60.20  
  Purchase #3 $161.92   9.467%   $177.249   $177.25   $177.25   $177.20  
  Purchase #4 $23.71   13.747%   $26.9694   $26.97   $26.95   $27.00  
  Purchase #5 $131.80   11.613%   $147.1059   $147.11   $147.10   $147.10  
  Purchase #6 $170.93   9.306%   $186.8367   $186.84   $186.85   $186.80  
  Purchase #7 $10.39   9.155%   $11.3412   $11.34   $11.35   $11.30  
  7 purchase totals = $615.50       $676.0152   $676.02   $676.00   $675.90