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 $175.67   6.271%   $186.6863   $186.69   $186.70   $186.70  
  Purchase #2 $164.94   3.181%   $170.1867   $170.19   $170.20   $170.20  
  Purchase #3 $212.96   7.653%   $229.2578   $229.26   $229.25   $229.30  
  Purchase #4 $162.61   9.458%   $177.9897   $177.99   $178.00   $178.00  
  Purchase #5 $79.95   8.821%   $87.0024   $87.00   $87.00   $87.00  
  Purchase #6 $170.67   8.819%   $185.7214   $185.72   $185.70   $185.70  
  Purchase #7 $11.44   3.179%   $11.8037   $11.80   $11.80   $11.80  
  7 purchase totals = $978.24       $1,048.6480   $1,048.65   $1,048.65   $1,048.70