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 $21.73   13.701%   $24.7072   $24.71   $24.70   $24.70  
  Purchase #2 $36.38   6.247%   $38.6527   $38.65   $38.65   $38.70  
  Purchase #3 $152.45   8.472%   $165.3656   $165.37   $165.35   $165.40  
  Purchase #4 $82.33   6.372%   $87.5761   $87.58   $87.60   $87.60  
  Purchase #5 $189.41   12.391%   $212.8798   $212.88   $212.90   $212.90  
  Purchase #6 $210.58   6.107%   $223.4401   $223.44   $223.45   $223.40  
  Purchase #7 $193.93   10.225%   $213.7593   $213.76   $213.75   $213.80  
  7 purchase totals = $886.81       $966.3808   $966.39   $966.40   $966.50