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 $184.71   3.722%   $191.5849   $191.58   $191.60   $191.60  
  Purchase #2 $97.70   6.149%   $103.7076   $103.71   $103.70   $103.70  
  Purchase #3 $160.25   3.333%   $165.5911   $165.59   $165.60   $165.60  
  Purchase #4 $102.36   4.197%   $106.656   $106.66   $106.65   $106.70  
  Purchase #5 $188.92   3.167%   $194.9031   $194.90   $194.90   $194.90  
  Purchase #6 $186.57   10.561%   $206.2737   $206.27   $206.25   $206.30  
  Purchase #7 $178.63   13.410%   $202.5843   $202.58   $202.60   $202.60  
  7 purchase totals = $1,099.14       $1,171.3007   $1,171.29   $1,171.30   $1,171.40