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 $60.35   11.514%   $67.2987   $67.30   $67.30   $67.30  
  Purchase #2 $164.57   9.184%   $179.6841   $179.68   $179.70   $179.70  
  Purchase #3 $182.86   12.598%   $205.8967   $205.90   $205.90   $205.90  
  Purchase #4 $139.37   5.805%   $147.4604   $147.46   $147.45   $147.50  
  Purchase #5 $104.69   5.804%   $110.7662   $110.77   $110.75   $110.80  
  Purchase #6 $169.87   6.628%   $181.129   $181.13   $181.15   $181.10  
  Purchase #7 $162.56   13.233%   $184.0716   $184.07   $184.05   $184.10  
  7 purchase totals = $984.27       $1,076.3067   $1,076.31   $1,076.30   $1,076.40