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 $218.68   10.643%   $241.9541   $241.95   $241.95   $242.00  
  Purchase #2 $116.52   6.646%   $124.2639   $124.26   $124.25   $124.30  
  Purchase #3 $102.25   4.463%   $106.8134   $106.81   $106.80   $106.80  
  Purchase #4 $145.98   8.419%   $158.2701   $158.27   $158.25   $158.30  
  Purchase #5 $111.73   12.699%   $125.9186   $125.92   $125.90   $125.90  
  Purchase #6 $30.33   6.464%   $32.2905   $32.29   $32.30   $32.30  
  Purchase #7 $88.32   7.652%   $95.0782   $95.08   $95.10   $95.10  
  7 purchase totals = $813.81       $884.5888   $884.58   $884.55   $884.70