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 $202.88   7.222%   $217.532   $217.53   $217.55   $217.50  
  Purchase #2 $56.80   9.151%   $61.9978   $62.00   $62.00   $62.00  
  Purchase #3 $61.87   11.106%   $68.7413   $68.74   $68.75   $68.70  
  Purchase #4 $115.93   13.497%   $131.5771   $131.58   $131.60   $131.60  
  Purchase #5 $227.76   11.237%   $253.3534   $253.35   $253.35   $253.40  
  Purchase #6 $188.69   9.856%   $207.2873   $207.29   $207.30   $207.30  
  Purchase #7 $229.32   12.552%   $258.1042   $258.10   $258.10   $258.10  
  7 purchase totals = $1,083.25       $1,198.5931   $1,198.59   $1,198.65   $1,198.60