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 $62.52   8.787%   $68.0136   $68.01   $68.00   $68.00  
  Purchase #2 $82.76   13.802%   $94.1825   $94.18   $94.20   $94.20  
  Purchase #3 $185.95   4.709%   $194.7064   $194.71   $194.70   $194.70  
  Purchase #4 $206.61   8.714%   $224.614   $224.61   $224.60   $224.60  
  Purchase #5 $176.32   6.645%   $188.0365   $188.04   $188.05   $188.00  
  Purchase #6 $65.80   9.493%   $72.0464   $72.05   $72.05   $72.00  
  Purchase #7 $18.95   3.294%   $19.5742   $19.57   $19.55   $19.60  
  7 purchase totals = $798.91       $861.1736   $861.17   $861.15   $861.10