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 $239.35   5.286%   $252.002   $252.00   $252.00   $252.00  
  Purchase #2 $32.48   9.483%   $35.5601   $35.56   $35.55   $35.60  
  Purchase #3 $74.55   10.848%   $82.6372   $82.64   $82.65   $82.60  
  Purchase #4 $133.77   9.720%   $146.7724   $146.77   $146.75   $146.80  
  Purchase #5 $156.87   12.423%   $176.358   $176.36   $176.35   $176.40  
  Purchase #6 $115.51   9.234%   $126.1762   $126.18   $126.20   $126.20  
  Purchase #7 $245.87   4.352%   $256.5703   $256.57   $256.55   $256.60  
  7 purchase totals = $998.40       $1,076.0762   $1,076.08   $1,076.05   $1,076.20