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 $96.48   13.839%   $109.8319   $109.83   $109.85   $109.80  
  Purchase #2 $172.28   6.562%   $183.585   $183.59   $183.60   $183.60  
  Purchase #3 $224.33   9.843%   $246.4108   $246.41   $246.40   $246.40  
  Purchase #4 $74.53   9.838%   $81.8623   $81.86   $81.85   $81.90  
  Purchase #5 $212.97   7.552%   $229.0535   $229.05   $229.05   $229.10  
  Purchase #6 $111.40   13.338%   $126.2585   $126.26   $126.25   $126.30  
  Purchase #7 $239.87   13.770%   $272.9001   $272.90   $272.90   $272.90  
  7 purchase totals = $1,131.86       $1,249.9021   $1,249.90   $1,249.90   $1,250.00