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 $58.70   4.323%   $61.2376   $61.24   $61.25   $61.20  
  Purchase #2 $176.60   3.657%   $183.0583   $183.06   $183.05   $183.10  
  Purchase #3 $94.44   10.456%   $104.3146   $104.31   $104.30   $104.30  
  Purchase #4 $22.35   5.177%   $23.5071   $23.51   $23.50   $23.50  
  Purchase #5 $163.78   3.631%   $169.7269   $169.73   $169.75   $169.70  
  Purchase #6 $197.45   12.720%   $222.5656   $222.57   $222.55   $222.60  
  Purchase #7 $10.49   12.687%   $11.8209   $11.82   $11.80   $11.80  
  7 purchase totals = $723.81       $776.2310   $776.24   $776.20   $776.20