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 $49.76   8.351%   $53.9155   $53.92   $53.90   $53.90  
  Purchase #2 $180.27   13.692%   $204.9526   $204.95   $204.95   $205.00  
  Purchase #3 $24.70   5.441%   $26.0439   $26.04   $26.05   $26.00  
  Purchase #4 $103.63   7.716%   $111.6261   $111.63   $111.65   $111.60  
  Purchase #5 $144.67   7.827%   $155.9933   $155.99   $156.00   $156.00  
  Purchase #6 $66.51   4.437%   $69.461   $69.46   $69.45   $69.50  
  Purchase #7 $204.61   4.502%   $213.8215   $213.82   $213.80   $213.80  
  7 purchase totals = $774.15       $835.8139   $835.81   $835.80   $835.80