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 $108.46   10.382%   $119.7203   $119.72   $119.70   $119.70  
  Purchase #2 $20.66   8.381%   $22.3915   $22.39   $22.40   $22.40  
  Purchase #3 $243.35   9.630%   $266.7846   $266.78   $266.80   $266.80  
  Purchase #4 $77.75   6.455%   $82.7688   $82.77   $82.75   $82.80  
  Purchase #5 $216.58   13.858%   $246.5937   $246.59   $246.60   $246.60  
  Purchase #6 $134.30   8.283%   $145.4241   $145.42   $145.40   $145.40  
  Purchase #7 $63.57   11.436%   $70.8399   $70.84   $70.85   $70.80  
  7 purchase totals = $864.67       $954.5229   $954.51   $954.50   $954.50