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 $216.45   4.499%   $226.1881   $226.19   $226.20   $226.20  
  Purchase #2 $98.36   12.278%   $110.4366   $110.44   $110.45   $110.40  
  Purchase #3 $147.30   11.570%   $164.3426   $164.34   $164.35   $164.30  
  Purchase #4 $180.87   13.641%   $205.5425   $205.54   $205.55   $205.50  
  Purchase #5 $241.30   8.293%   $261.311   $261.31   $261.30   $261.30  
  Purchase #6 $45.91   13.279%   $52.0064   $52.01   $52.00   $52.00  
  Purchase #7 $243.73   6.393%   $259.3117   $259.31   $259.30   $259.30  
  7 purchase totals = $1,173.92       $1,279.1389   $1,279.14   $1,279.15   $1,279.00