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 $181.28   10.658%   $200.6008   $200.60   $200.60   $200.60  
  Purchase #2 $165.63   3.203%   $170.9351   $170.94   $170.95   $170.90  
  Purchase #3 $236.40   11.490%   $263.5624   $263.56   $263.55   $263.60  
  Purchase #4 $64.91   5.582%   $68.5333   $68.53   $68.55   $68.50  
  Purchase #5 $155.51   13.279%   $176.1602   $176.16   $176.15   $176.20  
  Purchase #6 $244.50   3.402%   $252.8179   $252.82   $252.80   $252.80  
  Purchase #7 $27.31   12.107%   $30.6164   $30.62   $30.60   $30.60  
  7 purchase totals = $1,075.54       $1,163.2261   $1,163.23   $1,163.20   $1,163.20