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 $230.36   7.642%   $247.9641   $247.96   $247.95   $248.00  
  Purchase #2 $243.58   11.784%   $272.2835   $272.28   $272.30   $272.30  
  Purchase #3 $11.59   3.500%   $11.9957   $12.00   $12.00   $12.00  
  Purchase #4 $97.91   5.146%   $102.9484   $102.95   $102.95   $102.90  
  Purchase #5 $135.91   6.396%   $144.6028   $144.60   $144.60   $144.60  
  Purchase #6 $175.42   11.707%   $195.9564   $195.96   $195.95   $196.00  
  Purchase #7 $49.54   4.767%   $51.9016   $51.90   $51.90   $51.90  
  7 purchase totals = $944.31       $1,027.6525   $1,027.65   $1,027.65   $1,027.70