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 $241.97   11.224%   $269.1287   $269.13   $269.15   $269.10  
  Purchase #2 $175.87   7.490%   $189.0427   $189.04   $189.05   $189.00  
  Purchase #3 $40.98   5.139%   $43.086   $43.09   $43.10   $43.10  
  Purchase #4 $121.51   3.466%   $125.7215   $125.72   $125.70   $125.70  
  Purchase #5 $245.46   9.186%   $268.008   $268.01   $268.00   $268.00  
  Purchase #6 $118.30   5.333%   $124.6089   $124.61   $124.60   $124.60  
  Purchase #7 $149.26   5.506%   $157.4783   $157.48   $157.50   $157.50  
  7 purchase totals = $1,093.35       $1,177.0741   $1,177.08   $1,177.10   $1,177.00