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 $65.95   6.121%   $69.9868   $69.99   $70.00   $70.00  
  Purchase #2 $176.59   7.677%   $190.1468   $190.15   $190.15   $190.10  
  Purchase #3 $246.87   12.297%   $277.2276   $277.23   $277.25   $277.20  
  Purchase #4 $44.94   13.827%   $51.1539   $51.15   $51.15   $51.20  
  Purchase #5 $84.33   7.237%   $90.433   $90.43   $90.45   $90.40  
  Purchase #6 $24.55   7.561%   $26.4062   $26.41   $26.40   $26.40  
  Purchase #7 $57.42   12.126%   $64.3827   $64.38   $64.40   $64.40  
  7 purchase totals = $700.65       $769.7370   $769.74   $769.80   $769.70