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 $56.43   8.625%   $61.2971   $61.30   $61.30   $61.30  
  Purchase #2 $49.45   11.370%   $55.0725   $55.07   $55.05   $55.10  
  Purchase #3 $166.48   6.361%   $177.0698   $177.07   $177.05   $177.10  
  Purchase #4 $220.65   11.237%   $245.4444   $245.44   $245.45   $245.40  
  Purchase #5 $103.91   4.219%   $108.294   $108.29   $108.30   $108.30  
  Purchase #6 $213.35   5.245%   $224.5402   $224.54   $224.55   $224.50  
  Purchase #7 $22.71   11.312%   $25.279   $25.28   $25.30   $25.30  
  7 purchase totals = $832.98       $896.9970   $896.99   $897.00   $897.00