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 $54.73   8.447%   $59.353   $59.35   $59.35   $59.40  
  Purchase #2 $58.96   4.397%   $61.5525   $61.55   $61.55   $61.60  
  Purchase #3 $98.29   5.771%   $103.9623   $103.96   $103.95   $104.00  
  Purchase #4 $52.89   13.842%   $60.211   $60.21   $60.20   $60.20  
  Purchase #5 $66.91   13.470%   $75.9228   $75.92   $75.90   $75.90  
  Purchase #6 $216.97   4.329%   $226.3626   $226.36   $226.35   $226.40  
  Purchase #7 $81.55   5.852%   $86.3223   $86.32   $86.30   $86.30  
  7 purchase totals = $630.30       $673.6865   $673.67   $673.60   $673.80