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 $104.99   12.856%   $118.4875   $118.49   $118.50   $118.50  
  Purchase #2 $22.25   8.115%   $24.0556   $24.06   $24.05   $24.10  
  Purchase #3 $113.77   5.386%   $119.8977   $119.90   $119.90   $119.90  
  Purchase #4 $223.95   5.382%   $236.003   $236.00   $236.00   $236.00  
  Purchase #5 $112.27   9.145%   $122.5371   $122.54   $122.55   $122.50  
  Purchase #6 $165.72   6.170%   $175.9449   $175.94   $175.95   $175.90  
  Purchase #7 $125.40   3.107%   $129.2962   $129.30   $129.30   $129.30  
  7 purchase totals = $868.35       $926.2220   $926.23   $926.25   $926.20