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 $41.95   9.808%   $46.0645   $46.06   $46.05   $46.10  
  Purchase #2 $134.40   12.373%   $151.0293   $151.03   $151.05   $151.00  
  Purchase #3 $166.87   5.415%   $175.906   $175.91   $175.90   $175.90  
  Purchase #4 $12.25   13.146%   $13.8604   $13.86   $13.85   $13.90  
  Purchase #5 $69.83   13.197%   $79.0455   $79.05   $79.05   $79.00  
  Purchase #6 $246.59   9.719%   $270.5561   $270.56   $270.55   $270.60  
  Purchase #7 $100.69   8.730%   $109.4802   $109.48   $109.50   $109.50  
  7 purchase totals = $772.58       $845.9420   $845.95   $845.95   $846.00