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 $196.91   8.626%   $213.8955   $213.90   $213.90   $213.90  
  Purchase #2 $135.87   8.674%   $147.6554   $147.66   $147.65   $147.70  
  Purchase #3 $234.30   8.205%   $253.5243   $253.52   $253.50   $253.50  
  Purchase #4 $203.76   9.296%   $222.7015   $222.70   $222.70   $222.70  
  Purchase #5 $193.68   11.667%   $216.2766   $216.28   $216.30   $216.30  
  Purchase #6 $61.58   11.318%   $68.5496   $68.55   $68.55   $68.50  
  Purchase #7 $31.34   8.484%   $33.9989   $34.00   $34.00   $34.00  
  7 purchase totals = $1,057.44       $1,156.6018   $1,156.61   $1,156.60   $1,156.60