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 $64.56   10.676%   $71.4524   $71.45   $71.45   $71.50  
  Purchase #2 $197.58   5.119%   $207.6941   $207.69   $207.70   $207.70  
  Purchase #3 $206.89   9.699%   $226.9563   $226.96   $226.95   $227.00  
  Purchase #4 $187.36   9.264%   $204.717   $204.72   $204.70   $204.70  
  Purchase #5 $124.65   6.389%   $132.6139   $132.61   $132.60   $132.60  
  Purchase #6 $233.94   7.336%   $251.1018   $251.10   $251.10   $251.10  
  Purchase #7 $196.35   4.456%   $205.0994   $205.10   $205.10   $205.10  
  7 purchase totals = $1,211.33       $1,299.6349   $1,299.63   $1,299.60   $1,299.70