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 $248.58   5.852%   $263.1269   $263.13   $263.15   $263.10  
  Purchase #2 $193.43   3.262%   $199.7397   $199.74   $199.75   $199.70  
  Purchase #3 $154.34   13.838%   $175.6976   $175.70   $175.70   $175.70  
  Purchase #4 $172.70   10.438%   $190.7264   $190.73   $190.75   $190.70  
  Purchase #5 $89.58   8.154%   $96.8844   $96.88   $96.90   $96.90  
  Purchase #6 $45.34   11.421%   $50.5183   $50.52   $50.50   $50.50  
  Purchase #7 $32.81   8.842%   $35.7111   $35.71   $35.70   $35.70  
  7 purchase totals = $936.78       $1,012.4044   $1,012.41   $1,012.45   $1,012.30