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 $239.28   12.745%   $269.7762   $269.78   $269.80   $269.80  
  Purchase #2 $47.93   10.591%   $53.0063   $53.01   $53.00   $53.00  
  Purchase #3 $147.78   4.339%   $154.1922   $154.19   $154.20   $154.20  
  Purchase #4 $150.91   10.776%   $167.1721   $167.17   $167.15   $167.20  
  Purchase #5 $75.92   4.205%   $79.1124   $79.11   $79.10   $79.10  
  Purchase #6 $103.96   13.188%   $117.6702   $117.67   $117.65   $117.70  
  Purchase #7 $173.81   5.847%   $183.9727   $183.97   $183.95   $184.00  
  7 purchase totals = $939.59       $1,024.9021   $1,024.90   $1,024.85   $1,025.00