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 $29.26   13.506%   $33.2119   $33.21   $33.20   $33.20  
  Purchase #2 $220.45   9.594%   $241.6   $241.60   $241.60   $241.60  
  Purchase #3 $245.37   6.177%   $260.5265   $260.53   $260.55   $260.50  
  Purchase #4 $77.74   13.841%   $88.5   $88.50   $88.50   $88.50  
  Purchase #5 $214.69   5.390%   $226.2618   $226.26   $226.25   $226.30  
  Purchase #6 $238.37   10.630%   $263.7087   $263.71   $263.70   $263.70  
  Purchase #7 $33.71   3.696%   $34.9559   $34.96   $34.95   $35.00  
  7 purchase totals = $1,059.59       $1,148.7648   $1,148.77   $1,148.75   $1,148.80