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 $24.59   10.773%   $27.2391   $27.24   $27.25   $27.20  
  Purchase #2 $14.36   9.419%   $15.7126   $15.71   $15.70   $15.70  
  Purchase #3 $94.56   9.748%   $103.7777   $103.78   $103.80   $103.80  
  Purchase #4 $91.67   6.379%   $97.5176   $97.52   $97.50   $97.50  
  Purchase #5 $226.49   13.174%   $256.3278   $256.33   $256.35   $256.30  
  Purchase #6 $241.59   13.634%   $274.5284   $274.53   $274.55   $274.50  
  Purchase #7 $236.71   6.274%   $251.5612   $251.56   $251.55   $251.60  
  7 purchase totals = $929.97       $1,026.6644   $1,026.67   $1,026.70   $1,026.60