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 $8.44   7.588%   $9.0804   $9.08   $9.10   $9.10  
  Purchase #2 $167.45   6.768%   $178.783   $178.78   $178.80   $178.80  
  Purchase #3 $49.69   8.859%   $54.092   $54.09   $54.10   $54.10  
  Purchase #4 $220.47   7.478%   $236.9567   $236.96   $236.95   $237.00  
  Purchase #5 $100.38   8.726%   $109.1392   $109.14   $109.15   $109.10  
  Purchase #6 $15.85   9.404%   $17.3405   $17.34   $17.35   $17.30  
  Purchase #7 $220.81   4.618%   $231.007   $231.01   $231.00   $231.00  
  7 purchase totals = $783.09       $836.3988   $836.40   $836.45   $836.40