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 $54.43   12.414%   $61.1869   $61.19   $61.20   $61.20  
  Purchase #2 $76.53   7.652%   $82.3861   $82.39   $82.40   $82.40  
  Purchase #3 $218.85   8.481%   $237.4107   $237.41   $237.40   $237.40  
  Purchase #4 $45.33   9.488%   $49.6309   $49.63   $49.65   $49.60  
  Purchase #5 $29.95   9.612%   $32.8288   $32.83   $32.85   $32.80  
  Purchase #6 $222.97   6.822%   $238.181   $238.18   $238.20   $238.20  
  Purchase #7 $231.52   9.307%   $253.0676   $253.07   $253.05   $253.10  
  7 purchase totals = $879.58       $954.6920   $954.70   $954.75   $954.70