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 $152.99   10.487%   $169.0341   $169.03   $169.05   $169.00  
  Purchase #2 $143.29   8.854%   $155.9769   $155.98   $156.00   $156.00  
  Purchase #3 $243.80   10.395%   $269.143   $269.14   $269.15   $269.10  
  Purchase #4 $15.76   11.346%   $17.5481   $17.55   $17.55   $17.50  
  Purchase #5 $52.48   6.665%   $55.9778   $55.98   $56.00   $56.00  
  Purchase #6 $22.84   11.635%   $25.4974   $25.50   $25.50   $25.50  
  Purchase #7 $81.55   13.575%   $92.6204   $92.62   $92.60   $92.60  
  7 purchase totals = $712.71       $785.7977   $785.80   $785.85   $785.70