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 $115.76   6.768%   $123.5946   $123.59   $123.60   $123.60  
  Purchase #2 $178.61   9.173%   $194.9939   $194.99   $195.00   $195.00  
  Purchase #3 $233.76   9.858%   $256.8041   $256.80   $256.80   $256.80  
  Purchase #4 $197.70   6.213%   $209.9831   $209.98   $210.00   $210.00  
  Purchase #5 $167.67   7.590%   $180.3962   $180.40   $180.40   $180.40  
  Purchase #6 $175.51   6.186%   $186.367   $186.37   $186.35   $186.40  
  Purchase #7 $131.48   11.826%   $147.0288   $147.03   $147.05   $147.00  
  7 purchase totals = $1,200.49       $1,299.1677   $1,299.16   $1,299.20   $1,299.20