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 $88.56   8.578%   $96.1567   $96.16   $96.15   $96.20  
  Purchase #2 $169.93   3.165%   $175.3083   $175.31   $175.30   $175.30  
  Purchase #3 $60.32   11.401%   $67.1971   $67.20   $67.20   $67.20  
  Purchase #4 $172.72   10.167%   $190.2804   $190.28   $190.30   $190.30  
  Purchase #5 $106.96   7.594%   $115.0825   $115.08   $115.10   $115.10  
  Purchase #6 $93.55   10.680%   $103.5411   $103.54   $103.55   $103.50  
  Purchase #7 $61.99   6.738%   $66.1669   $66.17   $66.15   $66.20  
  7 purchase totals = $754.03       $813.7330   $813.74   $813.75   $813.80