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 $116.44   8.598%   $126.4515   $126.45   $126.45   $126.50  
  Purchase #2 $172.58   7.702%   $185.8721   $185.87   $185.85   $185.90  
  Purchase #3 $17.38   7.847%   $18.7438   $18.74   $18.75   $18.70  
  Purchase #4 $88.27   10.221%   $97.2921   $97.29   $97.30   $97.30  
  Purchase #5 $208.35   6.516%   $221.9261   $221.93   $221.95   $221.90  
  Purchase #6 $209.31   12.644%   $235.7752   $235.78   $235.80   $235.80  
  Purchase #7 $103.64   10.841%   $114.8756   $114.88   $114.90   $114.90  
  7 purchase totals = $915.97       $1,000.9364   $1,000.94   $1,001.00   $1,001.00