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 $23.49   11.758%   $26.252   $26.25   $26.25   $26.30  
  Purchase #2 $131.71   10.615%   $145.691   $145.69   $145.70   $145.70  
  Purchase #3 $73.76   9.470%   $80.7451   $80.75   $80.75   $80.70  
  Purchase #4 $53.98   10.841%   $59.832   $59.83   $59.85   $59.80  
  Purchase #5 $180.67   12.815%   $203.8229   $203.82   $203.80   $203.80  
  Purchase #6 $194.61   9.193%   $212.5005   $212.50   $212.50   $212.50  
  Purchase #7 $229.43   9.367%   $250.9207   $250.92   $250.90   $250.90  
  7 purchase totals = $887.65       $979.7642   $979.76   $979.75   $979.70