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 $50.34   6.757%   $53.7415   $53.74   $53.75   $53.70  
  Purchase #2 $61.84   4.419%   $64.5727   $64.57   $64.55   $64.60  
  Purchase #3 $57.78   5.604%   $61.018   $61.02   $61.00   $61.00  
  Purchase #4 $246.69   3.155%   $254.4731   $254.47   $254.45   $254.50  
  Purchase #5 $219.33   4.292%   $228.7436   $228.74   $228.75   $228.70  
  Purchase #6 $82.81   4.126%   $86.2267   $86.23   $86.25   $86.20  
  Purchase #7 $57.53   5.774%   $60.8518   $60.85   $60.85   $60.90  
  7 purchase totals = $776.32       $809.6274   $809.62   $809.60   $809.60