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 $61.72   8.255%   $66.815   $66.82   $66.80   $66.80  
  Purchase #2 $184.36   5.467%   $194.439   $194.44   $194.45   $194.40  
  Purchase #3 $120.48   9.280%   $131.6605   $131.66   $131.65   $131.70  
  Purchase #4 $177.60   10.638%   $196.4931   $196.49   $196.50   $196.50  
  Purchase #5 $69.48   6.540%   $74.024   $74.02   $74.00   $74.00  
  Purchase #6 $186.38   12.139%   $209.0047   $209.00   $209.00   $209.00  
  Purchase #7 $218.27   7.197%   $233.9789   $233.98   $234.00   $234.00  
  7 purchase totals = $1,018.29       $1,106.4152   $1,106.41   $1,106.40   $1,106.40