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 $204.79   8.780%   $222.7706   $222.77   $222.75   $222.80  
  Purchase #2 $211.87   13.462%   $240.3919   $240.39   $240.40   $240.40  
  Purchase #3 $150.84   11.258%   $167.8216   $167.82   $167.80   $167.80  
  Purchase #4 $107.54   7.492%   $115.5969   $115.60   $115.60   $115.60  
  Purchase #5 $77.80   10.397%   $85.8889   $85.89   $85.90   $85.90  
  Purchase #6 $86.62   12.381%   $97.3444   $97.34   $97.35   $97.30  
  Purchase #7 $115.51   12.659%   $130.1324   $130.13   $130.15   $130.10  
  7 purchase totals = $954.97       $1,059.9467   $1,059.94   $1,059.95   $1,059.90