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 $56.95   3.295%   $58.8265   $58.83   $58.85   $58.80  
  Purchase #2 $203.93   12.778%   $229.9882   $229.99   $230.00   $230.00  
  Purchase #3 $182.83   8.519%   $198.4053   $198.41   $198.40   $198.40  
  Purchase #4 $50.30   7.156%   $53.8995   $53.90   $53.90   $53.90  
  Purchase #5 $111.81   6.524%   $119.1045   $119.10   $119.10   $119.10  
  Purchase #6 $22.96   7.474%   $24.676   $24.68   $24.70   $24.70  
  Purchase #7 $73.71   6.297%   $78.3515   $78.35   $78.35   $78.40  
  7 purchase totals = $702.49       $763.2515   $763.26   $763.30   $763.30