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 $183.86   11.578%   $205.1473   $205.15   $205.15   $205.10  
  Purchase #2 $246.88   13.291%   $279.6928   $279.69   $279.70   $279.70  
  Purchase #3 $33.53   6.195%   $35.6072   $35.61   $35.60   $35.60  
  Purchase #4 $54.89   11.505%   $61.2051   $61.21   $61.20   $61.20  
  Purchase #5 $248.81   7.495%   $267.4583   $267.46   $267.45   $267.50  
  Purchase #6 $115.50   12.731%   $130.2043   $130.20   $130.20   $130.20  
  Purchase #7 $195.70   3.482%   $202.5143   $202.51   $202.50   $202.50  
  7 purchase totals = $1,079.17       $1,181.8293   $1,181.83   $1,181.80   $1,181.80