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 $66.61   5.168%   $70.0524   $70.05   $70.05   $70.10  
  Purchase #2 $218.86   12.765%   $246.7975   $246.80   $246.80   $246.80  
  Purchase #3 $96.43   8.231%   $104.3672   $104.37   $104.35   $104.40  
  Purchase #4 $163.29   13.739%   $185.7244   $185.72   $185.70   $185.70  
  Purchase #5 $48.32   7.115%   $51.758   $51.76   $51.75   $51.80  
  Purchase #6 $228.95   3.340%   $236.5969   $236.60   $236.60   $236.60  
  Purchase #7 $115.98   7.173%   $124.2992   $124.30   $124.30   $124.30  
  7 purchase totals = $938.44       $1,019.5956   $1,019.60   $1,019.55   $1,019.70