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 $248.38   11.390%   $276.6705   $276.67   $276.65   $276.70  
  Purchase #2 $51.90   3.394%   $53.6615   $53.66   $53.65   $53.70  
  Purchase #3 $153.56   13.612%   $174.4626   $174.46   $174.45   $174.50  
  Purchase #4 $229.80   8.183%   $248.6045   $248.60   $248.60   $248.60  
  Purchase #5 $160.94   9.772%   $176.6671   $176.67   $176.65   $176.70  
  Purchase #6 $64.89   11.416%   $72.2978   $72.30   $72.30   $72.30  
  Purchase #7 $77.55   3.763%   $80.4682   $80.47   $80.45   $80.50  
  7 purchase totals = $987.02       $1,082.8322   $1,082.83   $1,082.75   $1,083.00