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 $55.53   8.630%   $60.3222   $60.32   $60.30   $60.30  
  Purchase #2 $246.53   4.293%   $257.1135   $257.11   $257.10   $257.10  
  Purchase #3 $155.30   4.131%   $161.7154   $161.72   $161.70   $161.70  
  Purchase #4 $168.87   13.264%   $191.2689   $191.27   $191.25   $191.30  
  Purchase #5 $86.26   11.194%   $95.9159   $95.92   $95.90   $95.90  
  Purchase #6 $74.55   4.399%   $77.8295   $77.83   $77.85   $77.80  
  Purchase #7 $167.32   4.678%   $175.1472   $175.15   $175.15   $175.10  
  7 purchase totals = $954.36       $1,019.3126   $1,019.32   $1,019.25   $1,019.20