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 $223.36   8.211%   $241.7001   $241.70   $241.70   $241.70  
  Purchase #2 $51.86   9.588%   $56.8323   $56.83   $56.85   $56.80  
  Purchase #3 $190.45   9.819%   $209.1503   $209.15   $209.15   $209.20  
  Purchase #4 $53.88   13.809%   $61.3203   $61.32   $61.30   $61.30  
  Purchase #5 $147.67   4.257%   $153.9563   $153.96   $153.95   $154.00  
  Purchase #6 $40.49   9.417%   $44.3029   $44.30   $44.30   $44.30  
  Purchase #7 $96.73   13.109%   $109.4103   $109.41   $109.40   $109.40  
  7 purchase totals = $804.44       $876.6725   $876.67   $876.65   $876.70