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 $58.45   8.203%   $63.2447   $63.24   $63.25   $63.20  
  Purchase #2 $149.69   4.485%   $156.4036   $156.40   $156.40   $156.40  
  Purchase #3 $198.87   8.671%   $216.114   $216.11   $216.10   $216.10  
  Purchase #4 $48.40   8.790%   $52.6544   $52.65   $52.65   $52.70  
  Purchase #5 $209.27   6.632%   $223.1488   $223.15   $223.15   $223.10  
  Purchase #6 $34.61   3.585%   $35.8508   $35.85   $35.85   $35.90  
  Purchase #7 $9.86   4.256%   $10.2796   $10.28   $10.30   $10.30  
  7 purchase totals = $709.15       $757.6959   $757.68   $757.70   $757.70