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 $129.86   12.247%   $145.764   $145.76   $145.75   $145.80  
  Purchase #2 $226.43   8.610%   $245.9256   $245.93   $245.95   $245.90  
  Purchase #3 $48.34   4.626%   $50.5762   $50.58   $50.60   $50.60  
  Purchase #4 $248.71   6.412%   $264.6573   $264.66   $264.65   $264.70  
  Purchase #5 $162.59   5.828%   $172.0657   $172.07   $172.05   $172.10  
  Purchase #6 $154.44   5.668%   $163.1937   $163.19   $163.20   $163.20  
  Purchase #7 $19.39   11.784%   $21.6749   $21.67   $21.65   $21.70  
  7 purchase totals = $989.76       $1,063.8574   $1,063.86   $1,063.85   $1,064.00