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 $247.80   7.869%   $267.2994   $267.30   $267.30   $267.30  
  Purchase #2 $11.96   4.419%   $12.4885   $12.49   $12.50   $12.50  
  Purchase #3 $65.59   8.670%   $71.2767   $71.28   $71.30   $71.30  
  Purchase #4 $111.61   8.324%   $120.9004   $120.90   $120.90   $120.90  
  Purchase #5 $41.95   11.566%   $46.8019   $46.80   $46.80   $46.80  
  Purchase #6 $149.31   11.322%   $166.2149   $166.21   $166.20   $166.20  
  Purchase #7 $63.69   6.286%   $67.6936   $67.69   $67.70   $67.70  
  7 purchase totals = $691.91       $752.6754   $752.67   $752.70   $752.70