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 $61.40   12.736%   $69.2199   $69.22   $69.20   $69.20  
  Purchase #2 $87.53   7.252%   $93.8777   $93.88   $93.90   $93.90  
  Purchase #3 $25.92   12.199%   $29.082   $29.08   $29.10   $29.10  
  Purchase #4 $105.79   11.577%   $118.0373   $118.04   $118.05   $118.00  
  Purchase #5 $209.93   13.833%   $238.9696   $238.97   $238.95   $239.00  
  Purchase #6 $31.68   13.292%   $35.8909   $35.89   $35.90   $35.90  
  Purchase #7 $179.45   6.102%   $190.4   $190.40   $190.40   $190.40  
  7 purchase totals = $701.70       $775.4774   $775.48   $775.50   $775.50