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 $244.56   13.673%   $277.9987   $278.00   $278.00   $278.00  
  Purchase #2 $15.51   3.709%   $16.0853   $16.09   $16.10   $16.10  
  Purchase #3 $19.67   12.733%   $22.1746   $22.17   $22.15   $22.20  
  Purchase #4 $61.36   8.483%   $66.5652   $66.57   $66.55   $66.60  
  Purchase #5 $204.82   3.737%   $212.4741   $212.47   $212.45   $212.50  
  Purchase #6 $38.27   13.242%   $43.3377   $43.34   $43.35   $43.30  
  Purchase #7 $47.48   12.663%   $53.4924   $53.49   $53.50   $53.50  
  7 purchase totals = $631.67       $692.1280   $692.13   $692.10   $692.20