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 $86.46   6.244%   $91.8586   $91.86   $91.85   $91.90  
  Purchase #2 $70.65   3.825%   $73.3524   $73.35   $73.35   $73.40  
  Purchase #3 $33.99   11.513%   $37.9033   $37.90   $37.90   $37.90  
  Purchase #4 $245.62   4.718%   $257.2084   $257.21   $257.20   $257.20  
  Purchase #5 $189.76   7.439%   $203.8762   $203.88   $203.90   $203.90  
  Purchase #6 $120.72   7.548%   $129.8319   $129.83   $129.85   $129.80  
  Purchase #7 $54.82   11.278%   $61.0026   $61.00   $61.00   $61.00  
  7 purchase totals = $802.02       $855.0334   $855.03   $855.05   $855.10