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 $23.47   5.624%   $24.79   $24.79   $24.80   $24.80  
  Purchase #2 $38.45   8.355%   $41.6625   $41.66   $41.65   $41.70  
  Purchase #3 $22.69   5.721%   $23.9881   $23.99   $24.00   $24.00  
  Purchase #4 $106.60   3.657%   $110.4984   $110.50   $110.50   $110.50  
  Purchase #5 $214.48   4.406%   $223.93   $223.93   $223.95   $223.90  
  Purchase #6 $128.35   11.860%   $143.5723   $143.57   $143.55   $143.60  
  Purchase #7 $61.74   7.677%   $66.4798   $66.48   $66.50   $66.50  
  7 purchase totals = $595.78       $634.9211   $634.92   $634.95   $635.00