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 $52.41   8.712%   $56.976   $56.98   $57.00   $57.00  
  Purchase #2 $82.30   4.495%   $85.9994   $86.00   $86.00   $86.00  
  Purchase #3 $180.70   7.106%   $193.5405   $193.54   $193.55   $193.50  
  Purchase #4 $61.45   9.108%   $67.0469   $67.05   $67.05   $67.00  
  Purchase #5 $95.69   3.600%   $99.1348   $99.13   $99.15   $99.10  
  Purchase #6 $133.62   8.499%   $144.9764   $144.98   $145.00   $145.00  
  Purchase #7 $53.27   10.534%   $58.8815   $58.88   $58.90   $58.90  
  7 purchase totals = $659.44       $706.5555   $706.56   $706.65   $706.50