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 $38.44   12.260%   $43.1527   $43.15   $43.15   $43.20  
  Purchase #2 $226.39   8.547%   $245.7396   $245.74   $245.75   $245.70  
  Purchase #3 $219.64   8.626%   $238.5861   $238.59   $238.60   $238.60  
  Purchase #4 $179.29   6.379%   $190.7269   $190.73   $190.75   $190.70  
  Purchase #5 $206.54   9.595%   $226.3575   $226.36   $226.35   $226.40  
  Purchase #6 $238.61   12.401%   $268.2   $268.20   $268.20   $268.20  
  Purchase #7 $54.60   7.221%   $58.5427   $58.54   $58.55   $58.50  
  7 purchase totals = $1,163.51       $1,271.3055   $1,271.31   $1,271.35   $1,271.30