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 $39.93   8.764%   $43.4295   $43.43   $43.45   $43.40  
  Purchase #2 $67.63   12.789%   $76.2792   $76.28   $76.30   $76.30  
  Purchase #3 $168.38   7.874%   $181.6382   $181.64   $181.65   $181.60  
  Purchase #4 $58.81   3.200%   $60.6919   $60.69   $60.70   $60.70  
  Purchase #5 $170.87   13.599%   $194.1066   $194.11   $194.10   $194.10  
  Purchase #6 $108.82   10.587%   $120.3408   $120.34   $120.35   $120.30  
  Purchase #7 $20.36   11.422%   $22.6855   $22.69   $22.70   $22.70  
  7 purchase totals = $634.80       $699.1717   $699.18   $699.25   $699.10