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 $8.45   5.843%   $8.9437   $8.94   $8.95   $8.90  
  Purchase #2 $226.61   11.660%   $253.0327   $253.03   $253.05   $253.00  
  Purchase #3 $44.43   4.112%   $46.257   $46.26   $46.25   $46.30  
  Purchase #4 $94.73   7.531%   $101.8641   $101.86   $101.85   $101.90  
  Purchase #5 $112.66   8.849%   $122.6293   $122.63   $122.65   $122.60  
  Purchase #6 $191.91   6.608%   $204.5914   $204.59   $204.60   $204.60  
  Purchase #7 $225.68   5.586%   $238.2865   $238.29   $238.30   $238.30  
  7 purchase totals = $904.47       $975.6047   $975.60   $975.65   $975.60