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 $110.80   13.795%   $126.0849   $126.08   $126.10   $126.10  
  Purchase #2 $230.46   9.633%   $252.6602   $252.66   $252.65   $252.70  
  Purchase #3 $60.46   8.840%   $65.8047   $65.80   $65.80   $65.80  
  Purchase #4 $28.65   9.179%   $31.2798   $31.28   $31.30   $31.30  
  Purchase #5 $118.98   9.505%   $130.289   $130.29   $130.30   $130.30  
  Purchase #6 $214.94   13.246%   $243.411   $243.41   $243.40   $243.40  
  Purchase #7 $94.34   6.401%   $100.3787   $100.38   $100.40   $100.40  
  7 purchase totals = $858.63       $949.9083   $949.90   $949.95   $950.00