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 $204.44   10.617%   $226.1454   $226.15   $226.15   $226.10  
  Purchase #2 $91.68   4.382%   $95.6974   $95.70   $95.70   $95.70  
  Purchase #3 $24.41   9.701%   $26.778   $26.78   $26.80   $26.80  
  Purchase #4 $219.83   13.414%   $249.318   $249.32   $249.30   $249.30  
  Purchase #5 $70.44   6.857%   $75.2701   $75.27   $75.25   $75.30  
  Purchase #6 $166.69   12.496%   $187.5196   $187.52   $187.50   $187.50  
  Purchase #7 $173.85   9.335%   $190.0789   $190.08   $190.10   $190.10  
  7 purchase totals = $951.34       $1,050.8074   $1,050.82   $1,050.80   $1,050.80