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 $218.94   12.446%   $246.1893   $246.19   $246.20   $246.20  
  Purchase #2 $97.59   3.824%   $101.3218   $101.32   $101.30   $101.30  
  Purchase #3 $91.94   9.406%   $100.5879   $100.59   $100.60   $100.60  
  Purchase #4 $95.52   12.232%   $107.204   $107.20   $107.20   $107.20  
  Purchase #5 $202.40   5.811%   $214.1615   $214.16   $214.15   $214.20  
  Purchase #6 $52.93   8.408%   $57.3804   $57.38   $57.40   $57.40  
  Purchase #7 $51.68   9.465%   $56.5715   $56.57   $56.55   $56.60  
  7 purchase totals = $811.00       $883.4164   $883.41   $883.40   $883.50