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 $22.76   7.716%   $24.5162   $24.52   $24.50   $24.50  
  Purchase #2 $95.41   11.567%   $106.4461   $106.45   $106.45   $106.40  
  Purchase #3 $53.77   8.830%   $58.5179   $58.52   $58.50   $58.50  
  Purchase #4 $55.51   3.461%   $57.4312   $57.43   $57.45   $57.40  
  Purchase #5 $57.69   3.606%   $59.7703   $59.77   $59.75   $59.80  
  Purchase #6 $232.87   10.695%   $257.7754   $257.78   $257.80   $257.80  
  Purchase #7 $191.75   10.493%   $211.8703   $211.87   $211.85   $211.90  
  7 purchase totals = $709.76       $776.3274   $776.34   $776.30   $776.30