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 $53.34   5.359%   $56.1985   $56.20   $56.20   $56.20  
  Purchase #2 $189.80   4.663%   $198.6504   $198.65   $198.65   $198.70  
  Purchase #3 $95.54   12.656%   $107.6315   $107.63   $107.65   $107.60  
  Purchase #4 $142.90   6.764%   $152.5658   $152.57   $152.55   $152.60  
  Purchase #5 $20.69   13.128%   $23.4062   $23.41   $23.40   $23.40  
  Purchase #6 $165.65   9.670%   $181.6684   $181.67   $181.65   $181.70  
  Purchase #7 $65.58   8.758%   $71.3235   $71.32   $71.30   $71.30  
  7 purchase totals = $733.50       $791.4443   $791.45   $791.40   $791.50