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 $114.68   8.662%   $124.6136   $124.61   $124.60   $124.60  
  Purchase #2 $23.76   5.848%   $25.1495   $25.15   $25.15   $25.10  
  Purchase #3 $99.26   3.742%   $102.9743   $102.97   $102.95   $103.00  
  Purchase #4 $173.50   5.241%   $182.5931   $182.59   $182.60   $182.60  
  Purchase #5 $141.80   13.204%   $160.5233   $160.52   $160.50   $160.50  
  Purchase #6 $231.48   5.415%   $244.0146   $244.01   $244.00   $244.00  
  Purchase #7 $81.83   7.838%   $88.2438   $88.24   $88.25   $88.20  
  7 purchase totals = $866.31       $928.1122   $928.09   $928.05   $928.00