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 $241.44   11.549%   $269.3239   $269.32   $269.30   $269.30  
  Purchase #2 $153.47   6.552%   $163.5254   $163.53   $163.55   $163.50  
  Purchase #3 $166.61   10.515%   $184.129   $184.13   $184.15   $184.10  
  Purchase #4 $168.61   12.365%   $189.4586   $189.46   $189.45   $189.50  
  Purchase #5 $193.56   11.207%   $215.2523   $215.25   $215.25   $215.30  
  Purchase #6 $250.54   6.830%   $267.6519   $267.65   $267.65   $267.70  
  Purchase #7 $122.82   9.115%   $134.015   $134.02   $134.00   $134.00  
  7 purchase totals = $1,297.05       $1,423.3561   $1,423.36   $1,423.35   $1,423.40