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 $196.80   11.538%   $219.5068   $219.51   $219.50   $219.50  
  Purchase #2 $44.52   3.384%   $46.0266   $46.03   $46.05   $46.00  
  Purchase #3 $88.99   4.138%   $92.6724   $92.67   $92.65   $92.70  
  Purchase #4 $233.39   13.737%   $265.4508   $265.45   $265.45   $265.50  
  Purchase #5 $238.93   9.141%   $260.7706   $260.77   $260.75   $260.80  
  Purchase #6 $49.63   13.821%   $56.4894   $56.49   $56.50   $56.50  
  Purchase #7 $237.99   13.154%   $269.2952   $269.30   $269.30   $269.30  
  7 purchase totals = $1,090.25       $1,210.2118   $1,210.22   $1,210.20   $1,210.30