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 $64.25   12.438%   $72.2414   $72.24   $72.25   $72.20  
  Purchase #2 $99.41   6.161%   $105.5347   $105.53   $105.55   $105.50  
  Purchase #3 $152.63   10.830%   $169.1598   $169.16   $169.15   $169.20  
  Purchase #4 $246.25   8.816%   $267.9594   $267.96   $267.95   $268.00  
  Purchase #5 $60.25   10.805%   $66.76   $66.76   $66.75   $66.80  
  Purchase #6 $173.83   10.183%   $191.5311   $191.53   $191.55   $191.50  
  Purchase #7 $199.32   9.825%   $218.9032   $218.90   $218.90   $218.90  
  7 purchase totals = $995.94       $1,092.0896   $1,092.08   $1,092.10   $1,092.10