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 $52.35   7.546%   $56.3003   $56.30   $56.30   $56.30  
  Purchase #2 $119.90   12.636%   $135.0506   $135.05   $135.05   $135.10  
  Purchase #3 $21.94   7.766%   $23.6439   $23.64   $23.65   $23.60  
  Purchase #4 $74.83   13.382%   $84.8438   $84.84   $84.85   $84.80  
  Purchase #5 $212.52   3.674%   $220.328   $220.33   $220.35   $220.30  
  Purchase #6 $55.54   3.409%   $57.4334   $57.43   $57.45   $57.40  
  Purchase #7 $137.27   11.818%   $153.4926   $153.49   $153.50   $153.50  
  7 purchase totals = $674.35       $731.0926   $731.08   $731.15   $731.00