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 $155.30   3.708%   $161.0585   $161.06   $161.05   $161.10  
  Purchase #2 $10.39   4.547%   $10.8624   $10.86   $10.85   $10.90  
  Purchase #3 $86.55   12.360%   $97.2476   $97.25   $97.25   $97.20  
  Purchase #4 $35.72   4.436%   $37.3045   $37.30   $37.30   $37.30  
  Purchase #5 $63.63   3.496%   $65.8545   $65.85   $65.85   $65.90  
  Purchase #6 $32.52   3.305%   $33.5948   $33.59   $33.60   $33.60  
  Purchase #7 $26.33   4.470%   $27.507   $27.51   $27.50   $27.50  
  7 purchase totals = $410.44       $433.4293   $433.42   $433.40   $433.50