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 $71.51   6.245%   $75.9758   $75.98   $76.00   $76.00  
  Purchase #2 $81.92   11.412%   $91.2687   $91.27   $91.25   $91.30  
  Purchase #3 $65.50   10.823%   $72.5891   $72.59   $72.60   $72.60  
  Purchase #4 $211.81   9.281%   $231.4681   $231.47   $231.45   $231.50  
  Purchase #5 $27.28   6.218%   $28.9763   $28.98   $29.00   $29.00  
  Purchase #6 $154.27   8.773%   $167.8041   $167.80   $167.80   $167.80  
  Purchase #7 $13.30   5.822%   $14.0743   $14.07   $14.05   $14.10  
  7 purchase totals = $625.59       $682.1564   $682.16   $682.15   $682.30