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 $52.68   5.806%   $55.7386   $55.74   $55.75   $55.70  
  Purchase #2 $223.55   13.230%   $253.1257   $253.13   $253.15   $253.10  
  Purchase #3 $151.72   13.193%   $171.7364   $171.74   $171.75   $171.70  
  Purchase #4 $25.92   3.846%   $26.9169   $26.92   $26.90   $26.90  
  Purchase #5 $130.87   8.567%   $142.0816   $142.08   $142.10   $142.10  
  Purchase #6 $138.25   3.780%   $143.4759   $143.48   $143.50   $143.50  
  Purchase #7 $13.39   4.755%   $14.0267   $14.03   $14.05   $14.00  
  7 purchase totals = $736.38       $807.1018   $807.12   $807.20   $807.00