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 $65.86   3.707%   $68.3014   $68.30   $68.30   $68.30  
  Purchase #2 $96.33   13.326%   $109.1669   $109.17   $109.15   $109.20  
  Purchase #3 $69.51   13.387%   $78.8153   $78.82   $78.80   $78.80  
  Purchase #4 $147.33   8.740%   $160.2066   $160.21   $160.20   $160.20  
  Purchase #5 $27.45   11.559%   $30.6229   $30.62   $30.60   $30.60  
  Purchase #6 $184.60   12.723%   $208.0867   $208.09   $208.10   $208.10  
  Purchase #7 $134.75   13.542%   $152.9978   $153.00   $153.00   $153.00  
  7 purchase totals = $725.83       $808.1976   $808.21   $808.15   $808.20