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 $119.50   9.626%   $131.0031   $131.00   $131.00   $131.00  
  Purchase #2 $217.78   5.768%   $230.3416   $230.34   $230.35   $230.30  
  Purchase #3 $20.38   9.552%   $22.3267   $22.33   $22.35   $22.30  
  Purchase #4 $153.29   11.718%   $171.2525   $171.25   $171.25   $171.30  
  Purchase #5 $94.35   5.287%   $99.3383   $99.34   $99.35   $99.30  
  Purchase #6 $11.25   13.529%   $12.772   $12.77   $12.75   $12.80  
  Purchase #7 $232.44   3.109%   $239.6666   $239.67   $239.65   $239.70  
  7 purchase totals = $848.99       $906.7008   $906.70   $906.70   $906.70