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 $58.53   6.698%   $62.4503   $62.45   $62.45   $62.50  
  Purchase #2 $170.89   11.626%   $190.7577   $190.76   $190.75   $190.80  
  Purchase #3 $230.98   4.127%   $240.5125   $240.51   $240.50   $240.50  
  Purchase #4 $42.30   13.640%   $48.0697   $48.07   $48.05   $48.10  
  Purchase #5 $214.88   12.170%   $241.0309   $241.03   $241.05   $241.00  
  Purchase #6 $24.43   6.248%   $25.9564   $25.96   $25.95   $26.00  
  Purchase #7 $227.58   12.578%   $256.205   $256.21   $256.20   $256.20  
  7 purchase totals = $969.59       $1,064.9825   $1,064.99   $1,064.95   $1,065.10