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 $152.36   6.762%   $162.6626   $162.66   $162.65   $162.70  
  Purchase #2 $16.73   4.832%   $17.5384   $17.54   $17.55   $17.50  
  Purchase #3 $163.34   3.719%   $169.4146   $169.41   $169.40   $169.40  
  Purchase #4 $145.73   13.798%   $165.8378   $165.84   $165.85   $165.80  
  Purchase #5 $193.52   7.474%   $207.9837   $207.98   $208.00   $208.00  
  Purchase #6 $77.80   5.823%   $82.3303   $82.33   $82.35   $82.30  
  Purchase #7 $48.88   13.188%   $55.3263   $55.33   $55.35   $55.30  
  7 purchase totals = $798.36       $861.0937   $861.09   $861.15   $861.00