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 $201.55   8.159%   $217.9945   $217.99   $218.00   $218.00  
  Purchase #2 $74.83   13.363%   $84.8295   $84.83   $84.85   $84.80  
  Purchase #3 $71.29   11.664%   $79.6053   $79.61   $79.60   $79.60  
  Purchase #4 $183.80   7.144%   $196.9307   $196.93   $196.95   $196.90  
  Purchase #5 $60.79   10.135%   $66.9511   $66.95   $66.95   $67.00  
  Purchase #6 $88.39   7.573%   $95.0838   $95.08   $95.10   $95.10  
  Purchase #7 $87.73   6.198%   $93.1675   $93.17   $93.15   $93.20  
  7 purchase totals = $768.38       $834.5624   $834.56   $834.60   $834.60