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 $226.89   11.703%   $253.4429   $253.44   $253.45   $253.40  
  Purchase #2 $91.54   7.192%   $98.1236   $98.12   $98.10   $98.10  
  Purchase #3 $63.36   10.107%   $69.7638   $69.76   $69.75   $69.80  
  Purchase #4 $36.86   5.316%   $38.8195   $38.82   $38.80   $38.80  
  Purchase #5 $100.72   5.824%   $106.5859   $106.59   $106.60   $106.60  
  Purchase #6 $241.43   3.130%   $248.9868   $248.99   $249.00   $249.00  
  Purchase #7 $59.74   10.572%   $66.0557   $66.06   $66.05   $66.10  
  7 purchase totals = $820.54       $881.7782   $881.78   $881.75   $881.80