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 $41.57   12.577%   $46.7983   $46.80   $46.80   $46.80  
  Purchase #2 $169.98   6.528%   $181.0763   $181.08   $181.10   $181.10  
  Purchase #3 $195.66   5.649%   $206.7128   $206.71   $206.70   $206.70  
  Purchase #4 $215.61   12.697%   $242.986   $242.99   $243.00   $243.00  
  Purchase #5 $102.58   5.593%   $108.3173   $108.32   $108.30   $108.30  
  Purchase #6 $165.51   6.868%   $176.8772   $176.88   $176.90   $176.90  
  Purchase #7 $28.57   12.656%   $32.1858   $32.19   $32.20   $32.20  
  7 purchase totals = $919.48       $994.9537   $994.97   $995.00   $995.00