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 $246.57   10.114%   $271.5081   $271.51   $271.50   $271.50  
  Purchase #2 $194.42   5.790%   $205.6769   $205.68   $205.70   $205.70  
  Purchase #3 $47.89   9.845%   $52.6048   $52.60   $52.60   $52.60  
  Purchase #4 $19.26   5.627%   $20.3438   $20.34   $20.35   $20.30  
  Purchase #5 $170.86   8.805%   $185.9042   $185.90   $185.90   $185.90  
  Purchase #6 $150.87   3.378%   $155.9664   $155.97   $155.95   $156.00  
  Purchase #7 $166.54   4.276%   $173.6613   $173.66   $173.65   $173.70  
  7 purchase totals = $996.41       $1,065.6655   $1,065.66   $1,065.65   $1,065.70