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 $216.86   5.299%   $228.3514   $228.35   $228.35   $228.40  
  Purchase #2 $29.98   8.522%   $32.5349   $32.53   $32.55   $32.50  
  Purchase #3 $31.33   12.547%   $35.261   $35.26   $35.25   $35.30  
  Purchase #4 $168.89   6.765%   $180.3154   $180.32   $180.30   $180.30  
  Purchase #5 $46.60   11.402%   $51.9133   $51.91   $51.90   $51.90  
  Purchase #6 $168.83   8.282%   $182.8125   $182.81   $182.80   $182.80  
  Purchase #7 $184.36   7.608%   $198.3861   $198.39   $198.40   $198.40  
  7 purchase totals = $846.85       $909.5746   $909.57   $909.55   $909.60