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 $57.91   5.532%   $61.1136   $61.11   $61.10   $61.10  
  Purchase #2 $240.53   13.440%   $272.8572   $272.86   $272.85   $272.90  
  Purchase #3 $158.70   13.228%   $179.6928   $179.69   $179.70   $179.70  
  Purchase #4 $225.78   10.283%   $248.997   $249.00   $249.00   $249.00  
  Purchase #5 $229.68   8.470%   $249.1339   $249.13   $249.15   $249.10  
  Purchase #6 $61.40   11.219%   $68.2885   $68.29   $68.30   $68.30  
  Purchase #7 $202.87   11.532%   $226.265   $226.27   $226.25   $226.30  
  7 purchase totals = $1,176.87       $1,306.3480   $1,306.35   $1,306.35   $1,306.40