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 $87.44   10.211%   $96.3685   $96.37   $96.35   $96.40  
  Purchase #2 $191.43   8.395%   $207.5005   $207.50   $207.50   $207.50  
  Purchase #3 $70.95   8.638%   $77.0787   $77.08   $77.10   $77.10  
  Purchase #4 $59.42   10.826%   $65.8528   $65.85   $65.85   $65.90  
  Purchase #5 $178.77   11.476%   $199.2856   $199.29   $199.30   $199.30  
  Purchase #6 $108.63   4.397%   $113.4065   $113.41   $113.40   $113.40  
  Purchase #7 $106.42   13.740%   $121.0421   $121.04   $121.05   $121.00  
  7 purchase totals = $803.06       $880.5347   $880.54   $880.55   $880.60