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 $182.43   12.603%   $205.4217   $205.42   $205.40   $205.40  
  Purchase #2 $48.37   13.301%   $54.8037   $54.80   $54.80   $54.80  
  Purchase #3 $169.61   4.779%   $177.7157   $177.72   $177.70   $177.70  
  Purchase #4 $171.25   9.521%   $187.5547   $187.55   $187.55   $187.60  
  Purchase #5 $158.53   11.119%   $176.157   $176.16   $176.15   $176.20  
  Purchase #6 $163.73   10.717%   $181.2769   $181.28   $181.30   $181.30  
  Purchase #7 $21.68   8.731%   $23.5729   $23.57   $23.55   $23.60  
  7 purchase totals = $915.60       $1,006.5026   $1,006.50   $1,006.45   $1,006.60