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 $244.53   11.519%   $272.6974   $272.70   $272.70   $272.70  
  Purchase #2 $52.41   4.204%   $54.6133   $54.61   $54.60   $54.60  
  Purchase #3 $164.46   10.471%   $181.6806   $181.68   $181.70   $181.70  
  Purchase #4 $86.58   8.629%   $94.051   $94.05   $94.05   $94.10  
  Purchase #5 $170.34   13.175%   $192.7823   $192.78   $192.80   $192.80  
  Purchase #6 $242.87   10.857%   $269.2384   $269.24   $269.25   $269.20  
  Purchase #7 $102.58   3.535%   $106.2062   $106.21   $106.20   $106.20  
  7 purchase totals = $1,063.77       $1,171.2692   $1,171.27   $1,171.30   $1,171.30