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 $214.88   13.679%   $244.2734   $244.27   $244.25   $244.30  
  Purchase #2 $77.91   11.750%   $87.0644   $87.06   $87.05   $87.10  
  Purchase #3 $139.65   3.718%   $144.8422   $144.84   $144.85   $144.80  
  Purchase #4 $126.44   10.817%   $140.117   $140.12   $140.10   $140.10  
  Purchase #5 $85.44   12.209%   $95.8714   $95.87   $95.85   $95.90  
  Purchase #6 $175.90   10.764%   $194.8339   $194.83   $194.85   $194.80  
  Purchase #7 $191.48   4.593%   $200.2747   $200.27   $200.25   $200.30  
  7 purchase totals = $1,011.70       $1,107.2770   $1,107.26   $1,107.20   $1,107.30