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 $71.33   7.482%   $76.6669   $76.67   $76.65   $76.70  
  Purchase #2 $197.58   12.699%   $222.6707   $222.67   $222.65   $222.70  
  Purchase #3 $69.55   6.276%   $73.915   $73.92   $73.90   $73.90  
  Purchase #4 $98.40   10.455%   $108.6877   $108.69   $108.70   $108.70  
  Purchase #5 $202.59   8.353%   $219.5123   $219.51   $219.50   $219.50  
  Purchase #6 $38.59   12.264%   $43.3227   $43.32   $43.30   $43.30  
  Purchase #7 $101.87   8.237%   $110.261   $110.26   $110.25   $110.30  
  7 purchase totals = $779.91       $855.0363   $855.04   $854.95   $855.10