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 $112.85   11.680%   $126.0309   $126.03   $126.05   $126.00  
  Purchase #2 $211.67   8.424%   $229.5011   $229.50   $229.50   $229.50  
  Purchase #3 $119.75   12.404%   $134.6038   $134.60   $134.60   $134.60  
  Purchase #4 $243.76   10.339%   $268.9623   $268.96   $268.95   $269.00  
  Purchase #5 $47.84   3.633%   $49.578   $49.58   $49.60   $49.60  
  Purchase #6 $52.64   8.873%   $57.3107   $57.31   $57.30   $57.30  
  Purchase #7 $71.42   12.270%   $80.1832   $80.18   $80.20   $80.20  
  7 purchase totals = $859.93       $946.1700   $946.16   $946.20   $946.20