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 $126.52   6.141%   $134.2896   $134.29   $134.30   $134.30  
  Purchase #2 $113.28   3.198%   $116.9027   $116.90   $116.90   $116.90  
  Purchase #3 $97.72   6.126%   $103.7063   $103.71   $103.70   $103.70  
  Purchase #4 $148.48   5.340%   $156.4088   $156.41   $156.40   $156.40  
  Purchase #5 $228.47   7.146%   $244.7965   $244.80   $244.80   $244.80  
  Purchase #6 $41.70   4.429%   $43.5469   $43.55   $43.55   $43.50  
  Purchase #7 $226.55   3.522%   $234.5291   $234.53   $234.55   $234.50  
  7 purchase totals = $982.72       $1,034.1799   $1,034.19   $1,034.20   $1,034.10