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 $247.32   6.742%   $263.9943   $263.99   $264.00   $264.00  
  Purchase #2 $207.96   5.770%   $219.9593   $219.96   $219.95   $220.00  
  Purchase #3 $12.69   9.166%   $13.8532   $13.85   $13.85   $13.90  
  Purchase #4 $48.40   6.387%   $51.4913   $51.49   $51.50   $51.50  
  Purchase #5 $56.53   3.397%   $58.4503   $58.45   $58.45   $58.50  
  Purchase #6 $52.67   8.631%   $57.2159   $57.22   $57.20   $57.20  
  Purchase #7 $35.88   3.203%   $37.0292   $37.03   $37.05   $37.00  
  7 purchase totals = $661.45       $701.9935   $701.99   $702.00   $702.10