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 $150.71   3.218%   $155.5598   $155.56   $155.55   $155.60  
  Purchase #2 $84.97   13.828%   $96.7197   $96.72   $96.70   $96.70  
  Purchase #3 $161.37   7.280%   $173.1177   $173.12   $173.10   $173.10  
  Purchase #4 $215.50   3.394%   $222.8141   $222.81   $222.80   $222.80  
  Purchase #5 $126.95   6.600%   $135.3287   $135.33   $135.35   $135.30  
  Purchase #6 $225.45   8.683%   $245.0258   $245.03   $245.05   $245.00  
  Purchase #7 $157.54   6.712%   $168.1141   $168.11   $168.10   $168.10  
  7 purchase totals = $1,122.49       $1,196.6799   $1,196.68   $1,196.65   $1,196.60