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 $10.59   8.304%   $11.4694   $11.47   $11.45   $11.50  
  Purchase #2 $218.91   12.464%   $246.1949   $246.19   $246.20   $246.20  
  Purchase #3 $230.61   11.864%   $257.9696   $257.97   $257.95   $258.00  
  Purchase #4 $217.76   12.806%   $245.6463   $245.65   $245.65   $245.60  
  Purchase #5 $207.90   4.739%   $217.7524   $217.75   $217.75   $217.80  
  Purchase #6 $177.94   4.560%   $186.0541   $186.05   $186.05   $186.10  
  Purchase #7 $140.33   6.206%   $149.0389   $149.04   $149.05   $149.00  
  7 purchase totals = $1,204.04       $1,314.1256   $1,314.12   $1,314.10   $1,314.20