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 $63.30   3.225%   $65.3414   $65.34   $65.35   $65.30  
  Purchase #2 $208.45   4.323%   $217.4613   $217.46   $217.45   $217.50  
  Purchase #3 $167.86   5.570%   $177.2098   $177.21   $177.20   $177.20  
  Purchase #4 $124.75   7.673%   $134.3221   $134.32   $134.30   $134.30  
  Purchase #5 $230.92   12.770%   $260.4085   $260.41   $260.40   $260.40  
  Purchase #6 $63.98   9.394%   $69.9903   $69.99   $70.00   $70.00  
  Purchase #7 $32.89   9.277%   $35.9412   $35.94   $35.95   $35.90  
  7 purchase totals = $892.15       $960.6746   $960.67   $960.65   $960.60