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 $118.73   6.252%   $126.153   $126.15   $126.15   $126.20  
  Purchase #2 $168.64   11.451%   $187.951   $187.95   $187.95   $188.00  
  Purchase #3 $91.60   4.413%   $95.6423   $95.64   $95.65   $95.60  
  Purchase #4 $240.52   6.491%   $256.1322   $256.13   $256.15   $256.10  
  Purchase #5 $100.95   8.775%   $109.8084   $109.81   $109.80   $109.80  
  Purchase #6 $14.35   9.436%   $15.7041   $15.70   $15.70   $15.70  
  Purchase #7 $166.97   11.194%   $185.6606   $185.66   $185.65   $185.70  
  7 purchase totals = $901.76       $977.0516   $977.04   $977.05   $977.10