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 $67.54   8.584%   $73.3376   $73.34   $73.35   $73.30  
  Purchase #2 $26.51   9.726%   $29.0884   $29.09   $29.10   $29.10  
  Purchase #3 $155.80   9.238%   $170.1928   $170.19   $170.20   $170.20  
  Purchase #4 $76.48   12.371%   $85.9413   $85.94   $85.95   $85.90  
  Purchase #5 $190.35   11.128%   $211.5321   $211.53   $211.55   $211.50  
  Purchase #6 $227.26   10.400%   $250.895   $250.90   $250.90   $250.90  
  Purchase #7 $39.55   3.830%   $41.0648   $41.06   $41.05   $41.10  
  7 purchase totals = $783.49       $862.0520   $862.05   $862.10   $862.00