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 $28.40   5.348%   $29.9188   $29.92   $29.90   $29.90  
  Purchase #2 $63.38   10.543%   $70.0622   $70.06   $70.05   $70.10  
  Purchase #3 $118.28   9.322%   $129.3061   $129.31   $129.30   $129.30  
  Purchase #4 $106.52   13.282%   $120.668   $120.67   $120.65   $120.70  
  Purchase #5 $105.79   8.544%   $114.8287   $114.83   $114.85   $114.80  
  Purchase #6 $36.88   11.613%   $41.1629   $41.16   $41.15   $41.20  
  Purchase #7 $174.94   9.212%   $191.0555   $191.06   $191.05   $191.10  
  7 purchase totals = $634.19       $697.0022   $697.01   $696.95   $697.10