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 $178.98   13.464%   $203.0779   $203.08   $203.10   $203.10  
  Purchase #2 $158.60   12.760%   $178.8374   $178.84   $178.85   $178.80  
  Purchase #3 $26.44   5.645%   $27.9325   $27.93   $27.95   $27.90  
  Purchase #4 $213.31   3.244%   $220.2298   $220.23   $220.25   $220.20  
  Purchase #5 $127.27   5.527%   $134.3042   $134.30   $134.30   $134.30  
  Purchase #6 $35.97   8.291%   $38.9523   $38.95   $38.95   $39.00  
  Purchase #7 $248.64   5.330%   $261.8925   $261.89   $261.90   $261.90  
  7 purchase totals = $989.21       $1,065.2266   $1,065.22   $1,065.30   $1,065.20