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 $105.75   9.337%   $115.6239   $115.62   $115.60   $115.60  
  Purchase #2 $245.53   8.745%   $267.0016   $267.00   $267.00   $267.00  
  Purchase #3 $82.84   7.801%   $89.3023   $89.30   $89.30   $89.30  
  Purchase #4 $38.99   4.533%   $40.7574   $40.76   $40.75   $40.80  
  Purchase #5 $227.46   4.216%   $237.0497   $237.05   $237.05   $237.00  
  Purchase #6 $232.35   5.731%   $245.666   $245.67   $245.65   $245.70  
  Purchase #7 $57.90   4.755%   $60.6531   $60.65   $60.65   $60.70  
  7 purchase totals = $990.82       $1,056.0540   $1,056.05   $1,056.00   $1,056.10