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 $237.92   6.232%   $252.7472   $252.75   $252.75   $252.70  
  Purchase #2 $144.89   10.670%   $160.3498   $160.35   $160.35   $160.30  
  Purchase #3 $71.89   12.453%   $80.8425   $80.84   $80.85   $80.80  
  Purchase #4 $239.98   7.433%   $257.8177   $257.82   $257.80   $257.80  
  Purchase #5 $76.81   7.521%   $82.5869   $82.59   $82.60   $82.60  
  Purchase #6 $196.84   7.266%   $211.1424   $211.14   $211.15   $211.10  
  Purchase #7 $153.95   4.682%   $161.1579   $161.16   $161.15   $161.20  
  7 purchase totals = $1,122.28       $1,206.6444   $1,206.65   $1,206.65   $1,206.50