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 $161.90   5.584%   $170.9405   $170.94   $170.95   $170.90  
  Purchase #2 $241.51   11.369%   $268.9673   $268.97   $268.95   $269.00  
  Purchase #3 $220.42   13.130%   $249.3611   $249.36   $249.35   $249.40  
  Purchase #4 $153.40   3.664%   $159.0206   $159.02   $159.00   $159.00  
  Purchase #5 $192.88   4.475%   $201.5114   $201.51   $201.50   $201.50  
  Purchase #6 $208.93   11.334%   $232.6101   $232.61   $232.60   $232.60  
  Purchase #7 $73.52   11.251%   $81.7917   $81.79   $81.80   $81.80  
  7 purchase totals = $1,252.56       $1,364.2027   $1,364.20   $1,364.15   $1,364.20