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 $237.31   13.638%   $269.6743   $269.67   $269.65   $269.70  
  Purchase #2 $96.67   9.207%   $105.5704   $105.57   $105.55   $105.60  
  Purchase #3 $119.79   10.510%   $132.3799   $132.38   $132.40   $132.40  
  Purchase #4 $209.34   5.490%   $220.8328   $220.83   $220.85   $220.80  
  Purchase #5 $105.96   4.264%   $110.4781   $110.48   $110.50   $110.50  
  Purchase #6 $207.44   9.424%   $226.9891   $226.99   $227.00   $227.00  
  Purchase #7 $107.41   11.573%   $119.8406   $119.84   $119.85   $119.80  
  7 purchase totals = $1,083.92       $1,185.7652   $1,185.76   $1,185.80   $1,185.80