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 $53.66   9.780%   $58.9079   $58.91   $58.90   $58.90  
  Purchase #2 $31.26   11.545%   $34.869   $34.87   $34.85   $34.90  
  Purchase #3 $112.75   9.312%   $123.2493   $123.25   $123.25   $123.20  
  Purchase #4 $149.81   4.575%   $156.6638   $156.66   $156.65   $156.70  
  Purchase #5 $73.85   6.396%   $78.5734   $78.57   $78.55   $78.60  
  Purchase #6 $145.29   12.799%   $163.8857   $163.89   $163.90   $163.90  
  Purchase #7 $91.44   7.397%   $98.2038   $98.20   $98.20   $98.20  
  7 purchase totals = $658.06       $714.3529   $714.35   $714.30   $714.40