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 $149.64   9.590%   $163.9905   $163.99   $164.00   $164.00  
  Purchase #2 $10.98   5.234%   $11.5547   $11.55   $11.55   $11.60  
  Purchase #3 $60.62   12.513%   $68.2054   $68.21   $68.20   $68.20  
  Purchase #4 $203.75   6.779%   $217.5622   $217.56   $217.55   $217.60  
  Purchase #5 $117.49   7.605%   $126.4251   $126.43   $126.45   $126.40  
  Purchase #6 $235.82   5.318%   $248.3609   $248.36   $248.35   $248.40  
  Purchase #7 $199.56   11.825%   $223.158   $223.16   $223.15   $223.20  
  7 purchase totals = $977.86       $1,059.2568   $1,059.26   $1,059.25   $1,059.40