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 $11.58   11.702%   $12.9351   $12.94   $12.95   $12.90  
  Purchase #2 $152.37   10.208%   $167.9239   $167.92   $167.90   $167.90  
  Purchase #3 $52.30   11.392%   $58.258   $58.26   $58.25   $58.30  
  Purchase #4 $175.34   10.325%   $193.4439   $193.44   $193.45   $193.40  
  Purchase #5 $65.46   4.137%   $68.1681   $68.17   $68.15   $68.20  
  Purchase #6 $237.56   5.324%   $250.2077   $250.21   $250.20   $250.20  
  Purchase #7 $84.45   12.109%   $94.6761   $94.68   $94.70   $94.70  
  7 purchase totals = $779.06       $845.6128   $845.62   $845.60   $845.60