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 $86.91   10.457%   $95.9982   $96.00   $96.00   $96.00  
  Purchase #2 $156.80   5.759%   $165.8301   $165.83   $165.85   $165.80  
  Purchase #3 $143.37   3.229%   $147.9994   $148.00   $148.00   $148.00  
  Purchase #4 $44.49   13.194%   $50.36   $50.36   $50.35   $50.40  
  Purchase #5 $46.28   5.401%   $48.7796   $48.78   $48.80   $48.80  
  Purchase #6 $74.80   3.595%   $77.4891   $77.49   $77.50   $77.50  
  Purchase #7 $234.45   4.630%   $245.305   $245.31   $245.30   $245.30  
  7 purchase totals = $787.10       $831.7614   $831.77   $831.80   $831.80