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 $202.93   10.230%   $223.6897   $223.69   $223.70   $223.70  
  Purchase #2 $163.74   4.828%   $171.6454   $171.65   $171.65   $171.60  
  Purchase #3 $160.89   13.350%   $182.3688   $182.37   $182.35   $182.40  
  Purchase #4 $67.46   3.716%   $69.9668   $69.97   $69.95   $70.00  
  Purchase #5 $29.74   3.555%   $30.7973   $30.80   $30.80   $30.80  
  Purchase #6 $112.66   11.556%   $125.679   $125.68   $125.70   $125.70  
  Purchase #7 $82.69   5.572%   $87.2975   $87.30   $87.30   $87.30  
  7 purchase totals = $820.11       $891.4445   $891.46   $891.45   $891.50