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 $116.67   5.623%   $123.2304   $123.23   $123.25   $123.20  
  Purchase #2 $206.44   9.524%   $226.1013   $226.10   $226.10   $226.10  
  Purchase #3 $89.37   8.122%   $96.6286   $96.63   $96.65   $96.60  
  Purchase #4 $154.96   12.639%   $174.5454   $174.55   $174.55   $174.50  
  Purchase #5 $93.94   12.253%   $105.4505   $105.45   $105.45   $105.50  
  Purchase #6 $241.68   11.109%   $268.5282   $268.53   $268.55   $268.50  
  Purchase #7 $77.28   7.807%   $83.3132   $83.31   $83.30   $83.30  
  7 purchase totals = $980.34       $1,077.7976   $1,077.80   $1,077.85   $1,077.70