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 $57.65   9.625%   $63.1988   $63.20   $63.20   $63.20  
  Purchase #2 $188.47   9.402%   $206.1899   $206.19   $206.20   $206.20  
  Purchase #3 $187.86   9.560%   $205.8194   $205.82   $205.80   $205.80  
  Purchase #4 $224.46   7.711%   $241.7681   $241.77   $241.75   $241.80  
  Purchase #5 $176.31   6.874%   $188.4295   $188.43   $188.45   $188.40  
  Purchase #6 $103.92   8.544%   $112.7989   $112.80   $112.80   $112.80  
  Purchase #7 $12.61   4.837%   $13.2199   $13.22   $13.20   $13.20  
  7 purchase totals = $951.28       $1,031.4245   $1,031.43   $1,031.40   $1,031.40