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 $106.31   13.367%   $120.5205   $120.52   $120.50   $120.50  
  Purchase #2 $44.39   8.378%   $48.109   $48.11   $48.10   $48.10  
  Purchase #3 $56.79   8.217%   $61.4564   $61.46   $61.45   $61.50  
  Purchase #4 $223.52   12.200%   $250.7894   $250.79   $250.80   $250.80  
  Purchase #5 $101.26   5.369%   $106.6966   $106.70   $106.70   $106.70  
  Purchase #6 $106.84   8.494%   $115.915   $115.92   $115.90   $115.90  
  Purchase #7 $196.64   5.519%   $207.4926   $207.49   $207.50   $207.50  
  7 purchase totals = $835.75       $910.9795   $910.99   $910.95   $911.00