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 $68.67   10.358%   $75.7828   $75.78   $75.80   $75.80  
  Purchase #2 $93.84   8.337%   $101.6634   $101.66   $101.65   $101.70  
  Purchase #3 $244.60   5.260%   $257.466   $257.47   $257.45   $257.50  
  Purchase #4 $27.60   11.252%   $30.7056   $30.71   $30.70   $30.70  
  Purchase #5 $242.69   11.638%   $270.9343   $270.93   $270.95   $270.90  
  Purchase #6 $105.81   6.850%   $113.058   $113.06   $113.05   $113.10  
  Purchase #7 $185.32   11.322%   $206.3019   $206.30   $206.30   $206.30  
  7 purchase totals = $968.53       $1,055.9120   $1,055.91   $1,055.90   $1,056.00