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 $64.58   7.320%   $69.3073   $69.31   $69.30   $69.30  
  Purchase #2 $144.48   11.782%   $161.5026   $161.50   $161.50   $161.50  
  Purchase #3 $206.70   9.595%   $226.5329   $226.53   $226.55   $226.50  
  Purchase #4 $143.56   8.123%   $155.2214   $155.22   $155.20   $155.20  
  Purchase #5 $136.46   8.382%   $147.8981   $147.90   $147.90   $147.90  
  Purchase #6 $57.45   11.482%   $64.0464   $64.05   $64.05   $64.00  
  Purchase #7 $212.94   9.614%   $233.4121   $233.41   $233.40   $233.40  
  7 purchase totals = $966.17       $1,057.9208   $1,057.92   $1,057.90   $1,057.80