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 $182.91   12.103%   $205.0476   $205.05   $205.05   $205.00  
  Purchase #2 $222.64   11.526%   $248.3015   $248.30   $248.30   $248.30  
  Purchase #3 $44.25   12.496%   $49.7795   $49.78   $49.80   $49.80  
  Purchase #4 $70.58   9.234%   $77.0974   $77.10   $77.10   $77.10  
  Purchase #5 $121.79   3.486%   $126.0356   $126.04   $126.05   $126.00  
  Purchase #6 $194.39   13.821%   $221.2566   $221.26   $221.25   $221.30  
  Purchase #7 $25.49   12.265%   $28.6163   $28.62   $28.60   $28.60  
  7 purchase totals = $862.05       $956.1345   $956.15   $956.15   $956.10