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 $155.69   5.283%   $163.9151   $163.92   $163.90   $163.90  
  Purchase #2 $228.78   12.326%   $256.9794   $256.98   $257.00   $257.00  
  Purchase #3 $49.56   8.246%   $53.6467   $53.65   $53.65   $53.60  
  Purchase #4 $232.91   6.298%   $247.5787   $247.58   $247.60   $247.60  
  Purchase #5 $162.52   3.661%   $168.4699   $168.47   $168.45   $168.50  
  Purchase #6 $206.92   4.270%   $215.7555   $215.76   $215.75   $215.80  
  Purchase #7 $216.29   4.863%   $226.8082   $226.81   $226.80   $226.80  
  7 purchase totals = $1,252.67       $1,333.1535   $1,333.17   $1,333.15   $1,333.20