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 $53.54   9.247%   $58.4908   $58.49   $58.50   $58.50  
  Purchase #2 $217.48   10.705%   $240.7612   $240.76   $240.75   $240.80  
  Purchase #3 $58.27   4.774%   $61.0518   $61.05   $61.05   $61.10  
  Purchase #4 $141.33   10.300%   $155.887   $155.89   $155.90   $155.90  
  Purchase #5 $137.70   8.337%   $149.18   $149.18   $149.20   $149.20  
  Purchase #6 $43.88   6.706%   $46.8226   $46.82   $46.80   $46.80  
  Purchase #7 $237.45   11.152%   $263.9304   $263.93   $263.95   $263.90  
  7 purchase totals = $889.65       $976.1238   $976.12   $976.15   $976.20