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 $11.27   11.322%   $12.546   $12.55   $12.55   $12.50  
  Purchase #2 $60.99   5.773%   $64.511   $64.51   $64.50   $64.50  
  Purchase #3 $113.39   4.628%   $118.6377   $118.64   $118.65   $118.60  
  Purchase #4 $65.49   7.728%   $70.5511   $70.55   $70.55   $70.60  
  Purchase #5 $236.74   9.313%   $258.7876   $258.79   $258.80   $258.80  
  Purchase #6 $151.27   9.615%   $165.8146   $165.81   $165.80   $165.80  
  Purchase #7 $41.41   6.646%   $44.1621   $44.16   $44.15   $44.20  
  7 purchase totals = $680.56       $735.0101   $735.01   $735.00   $735.00