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 $77.51   10.211%   $85.4245   $85.42   $85.40   $85.40  
  Purchase #2 $84.85   13.536%   $96.3353   $96.34   $96.35   $96.30  
  Purchase #3 $190.68   5.817%   $201.7719   $201.77   $201.75   $201.80  
  Purchase #4 $92.85   3.853%   $96.4275   $96.43   $96.45   $96.40  
  Purchase #5 $21.90   10.799%   $24.265   $24.27   $24.25   $24.30  
  Purchase #6 $185.80   8.463%   $201.5243   $201.52   $201.50   $201.50  
  Purchase #7 $224.80   12.234%   $252.302   $252.30   $252.30   $252.30  
  7 purchase totals = $878.39       $958.0505   $958.05   $958.00   $958.00