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 $58.39   8.218%   $63.1885   $63.19   $63.20   $63.20  
  Purchase #2 $117.36   3.830%   $121.8549   $121.85   $121.85   $121.90  
  Purchase #3 $93.55   8.827%   $101.8077   $101.81   $101.80   $101.80  
  Purchase #4 $116.51   7.547%   $125.303   $125.30   $125.30   $125.30  
  Purchase #5 $177.60   9.793%   $194.9924   $194.99   $195.00   $195.00  
  Purchase #6 $108.41   3.153%   $111.8282   $111.83   $111.85   $111.80  
  Purchase #7 $172.39   11.142%   $191.5977   $191.60   $191.60   $191.60  
  7 purchase totals = $844.21       $910.5724   $910.57   $910.60   $910.60