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 $57.69   6.238%   $61.2887   $61.29   $61.30   $61.30  
  Purchase #2 $246.43   5.696%   $260.4667   $260.47   $260.45   $260.50  
  Purchase #3 $222.41   11.565%   $248.1317   $248.13   $248.15   $248.10  
  Purchase #4 $176.92   5.846%   $187.2627   $187.26   $187.25   $187.30  
  Purchase #5 $60.94   10.108%   $67.0998   $67.10   $67.10   $67.10  
  Purchase #6 $205.87   6.713%   $219.6901   $219.69   $219.70   $219.70  
  Purchase #7 $246.63   9.585%   $270.2695   $270.27   $270.25   $270.30  
  7 purchase totals = $1,216.89       $1,314.2092   $1,314.21   $1,314.20   $1,314.30