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 $54.39   3.241%   $56.1528   $56.15   $56.15   $56.20  
  Purchase #2 $82.72   4.129%   $86.1355   $86.14   $86.15   $86.10  
  Purchase #3 $154.44   8.562%   $167.6632   $167.66   $167.65   $167.70  
  Purchase #4 $185.50   11.192%   $206.2612   $206.26   $206.25   $206.30  
  Purchase #5 $120.44   9.809%   $132.254   $132.25   $132.25   $132.30  
  Purchase #6 $232.43   5.534%   $245.2927   $245.29   $245.30   $245.30  
  Purchase #7 $163.62   6.637%   $174.4795   $174.48   $174.50   $174.50  
  7 purchase totals = $993.54       $1,068.2389   $1,068.23   $1,068.25   $1,068.40