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 $225.43   8.398%   $244.3616   $244.36   $244.35   $244.40  
  Purchase #2 $175.63   8.582%   $190.7026   $190.70   $190.70   $190.70  
  Purchase #3 $150.53   12.346%   $169.1144   $169.11   $169.10   $169.10  
  Purchase #4 $91.65   5.654%   $96.8319   $96.83   $96.85   $96.80  
  Purchase #5 $192.50   7.542%   $207.0184   $207.02   $207.00   $207.00  
  Purchase #6 $225.26   3.872%   $233.9821   $233.98   $234.00   $234.00  
  Purchase #7 $110.68   6.433%   $117.8   $117.80   $117.80   $117.80  
  7 purchase totals = $1,171.68       $1,259.8110   $1,259.80   $1,259.80   $1,259.80