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 $36.26   7.163%   $38.8573   $38.86   $38.85   $38.90  
  Purchase #2 $66.47   3.342%   $68.6914   $68.69   $68.70   $68.70  
  Purchase #3 $201.76   7.863%   $217.6244   $217.62   $217.60   $217.60  
  Purchase #4 $226.26   5.412%   $238.5052   $238.51   $238.50   $238.50  
  Purchase #5 $191.50   3.772%   $198.7234   $198.72   $198.70   $198.70  
  Purchase #6 $181.80   3.340%   $187.8721   $187.87   $187.85   $187.90  
  Purchase #7 $50.75   8.398%   $55.012   $55.01   $55.00   $55.00  
  7 purchase totals = $954.80       $1,005.2858   $1,005.28   $1,005.20   $1,005.30