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 $183.38   12.650%   $206.5776   $206.58   $206.60   $206.60  
  Purchase #2 $74.57   3.149%   $76.9182   $76.92   $76.90   $76.90  
  Purchase #3 $248.94   8.715%   $270.6351   $270.64   $270.65   $270.60  
  Purchase #4 $219.30   11.104%   $243.6511   $243.65   $243.65   $243.70  
  Purchase #5 $12.96   10.621%   $14.3365   $14.34   $14.35   $14.30  
  Purchase #6 $95.33   6.641%   $101.6609   $101.66   $101.65   $101.70  
  Purchase #7 $105.58   6.376%   $112.3118   $112.31   $112.30   $112.30  
  7 purchase totals = $940.06       $1,026.0912   $1,026.10   $1,026.10   $1,026.10