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 $149.52   8.358%   $162.0169   $162.02   $162.00   $162.00  
  Purchase #2 $182.79   5.738%   $193.2785   $193.28   $193.30   $193.30  
  Purchase #3 $249.32   11.316%   $277.5331   $277.53   $277.55   $277.50  
  Purchase #4 $157.62   7.695%   $169.7489   $169.75   $169.75   $169.70  
  Purchase #5 $9.45   9.714%   $10.368   $10.37   $10.35   $10.40  
  Purchase #6 $26.73   11.371%   $29.7695   $29.77   $29.75   $29.80  
  Purchase #7 $173.68   10.851%   $192.526   $192.53   $192.55   $192.50  
  7 purchase totals = $949.11       $1,035.2409   $1,035.25   $1,035.25   $1,035.20