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 $158.56   13.826%   $180.4825   $180.48   $180.50   $180.50  
  Purchase #2 $195.27   8.485%   $211.8387   $211.84   $211.85   $211.80  
  Purchase #3 $115.59   7.644%   $124.4257   $124.43   $124.45   $124.40  
  Purchase #4 $98.42   5.423%   $103.7573   $103.76   $103.75   $103.80  
  Purchase #5 $85.52   6.828%   $91.3593   $91.36   $91.35   $91.40  
  Purchase #6 $212.74   3.841%   $220.9113   $220.91   $220.90   $220.90  
  Purchase #7 $93.25   9.252%   $101.8775   $101.88   $101.90   $101.90  
  7 purchase totals = $959.35       $1,034.6523   $1,034.66   $1,034.70   $1,034.70